FCL/sf/os/fshell: libraries/spcre/libpcre/pcre/doc/html/pcrepattern.html@092bcc217d9d (annotated)

0 7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1	<html>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2	<head>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	3	<title>pcrepattern specification</title>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	4	</head>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	5	<body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB">
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	6	<h1>pcrepattern man page</h1>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	7	<p>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	8	Return to the <a href="index.html">PCRE index page</a>.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	9	</p>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	10	<p>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	11	This page is part of the PCRE HTML documentation. It was generated automatically
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	12	from the original man page. If there is any nonsense in it, please consult the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	13	man page, in case the conversion went wrong.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	14	<br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	15	<ul>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	16	<li><a name="TOC1" href="#SEC1">PCRE REGULAR EXPRESSION DETAILS</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	17	<li><a name="TOC2" href="#SEC2">NEWLINE CONVENTIONS</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	18	<li><a name="TOC3" href="#SEC3">CHARACTERS AND METACHARACTERS</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	19	<li><a name="TOC4" href="#SEC4">BACKSLASH</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	20	<li><a name="TOC5" href="#SEC5">CIRCUMFLEX AND DOLLAR</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	21	<li><a name="TOC6" href="#SEC6">FULL STOP (PERIOD, DOT)</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	22	<li><a name="TOC7" href="#SEC7">MATCHING A SINGLE BYTE</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	23	<li><a name="TOC8" href="#SEC8">SQUARE BRACKETS AND CHARACTER CLASSES</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	24	<li><a name="TOC9" href="#SEC9">POSIX CHARACTER CLASSES</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	25	<li><a name="TOC10" href="#SEC10">VERTICAL BAR</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	26	<li><a name="TOC11" href="#SEC11">INTERNAL OPTION SETTING</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	27	<li><a name="TOC12" href="#SEC12">SUBPATTERNS</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	28	<li><a name="TOC13" href="#SEC13">DUPLICATE SUBPATTERN NUMBERS</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	29	<li><a name="TOC14" href="#SEC14">NAMED SUBPATTERNS</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	30	<li><a name="TOC15" href="#SEC15">REPETITION</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	31	<li><a name="TOC16" href="#SEC16">ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	32	<li><a name="TOC17" href="#SEC17">BACK REFERENCES</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	33	<li><a name="TOC18" href="#SEC18">ASSERTIONS</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	34	<li><a name="TOC19" href="#SEC19">CONDITIONAL SUBPATTERNS</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	35	<li><a name="TOC20" href="#SEC20">COMMENTS</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	36	<li><a name="TOC21" href="#SEC21">RECURSIVE PATTERNS</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	37	<li><a name="TOC22" href="#SEC22">SUBPATTERNS AS SUBROUTINES</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	38	<li><a name="TOC23" href="#SEC23">ONIGURUMA SUBROUTINE SYNTAX</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	39	<li><a name="TOC24" href="#SEC24">CALLOUTS</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	40	<li><a name="TOC25" href="#SEC25">BACKTRACKING CONTROL</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	41	<li><a name="TOC26" href="#SEC26">SEE ALSO</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	42	<li><a name="TOC27" href="#SEC27">AUTHOR</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	43	<li><a name="TOC28" href="#SEC28">REVISION</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	44	</ul>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	45	<br><a name="SEC1" href="#TOC1">PCRE REGULAR EXPRESSION DETAILS</a><br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	46	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	47	The syntax and semantics of the regular expressions that are supported by PCRE
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	48	are described in detail below. There is a quick-reference syntax summary in the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	49	<a href="pcresyntax.html"><b>pcresyntax</b></a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	50	page. PCRE tries to match Perl syntax and semantics as closely as it can. PCRE
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	51	also supports some alternative regular expression syntax (which does not
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	52	conflict with the Perl syntax) in order to provide some compatibility with
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	53	regular expressions in Python, .NET, and Oniguruma.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	54	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	55	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	56	Perl's regular expressions are described in its own documentation, and
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	57	regular expressions in general are covered in a number of books, some of which
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	58	have copious examples. Jeffrey Friedl's "Mastering Regular Expressions",
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	59	published by O'Reilly, covers regular expressions in great detail. This
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	60	description of PCRE's regular expressions is intended as reference material.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	61	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	62	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	63	The original operation of PCRE was on strings of one-byte characters. However,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	64	there is now also support for UTF-8 character strings. To use this, you must
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	65	build PCRE to include UTF-8 support, and then call <b>pcre_compile()</b> with
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	66	the PCRE_UTF8 option. How this affects pattern matching is mentioned in several
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	67	places below. There is also a summary of UTF-8 features in the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	68	<a href="pcre.html#utf8support">section on UTF-8 support</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	69	in the main
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	70	<a href="pcre.html"><b>pcre</b></a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	71	page.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	72	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	73	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	74	The remainder of this document discusses the patterns that are supported by
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	75	PCRE when its main matching function, <b>pcre_exec()</b>, is used.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	76	From release 6.0, PCRE offers a second matching function,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	77	<b>pcre_dfa_exec()</b>, which matches using a different algorithm that is not
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	78	Perl-compatible. Some of the features discussed below are not available when
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	79	<b>pcre_dfa_exec()</b> is used. The advantages and disadvantages of the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	80	alternative function, and how it differs from the normal function, are
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	81	discussed in the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	82	<a href="pcrematching.html"><b>pcrematching</b></a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	83	page.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	84	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	85	<br><a name="SEC2" href="#TOC1">NEWLINE CONVENTIONS</a><br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	86	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	87	PCRE supports five different conventions for indicating line breaks in
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	88	strings: a single CR (carriage return) character, a single LF (linefeed)
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	89	character, the two-character sequence CRLF, any of the three preceding, or any
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	90	Unicode newline sequence. The
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	91	<a href="pcreapi.html"><b>pcreapi</b></a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	92	page has
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	93	<a href="pcreapi.html#newlines">further discussion</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	94	about newlines, and shows how to set the newline convention in the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	95	<i>options</i> arguments for the compiling and matching functions.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	96	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	97	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	98	It is also possible to specify a newline convention by starting a pattern
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	99	string with one of the following five sequences:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	100	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	101	(*CR) carriage return
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	102	(*LF) linefeed
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	103	(*CRLF) carriage return, followed by linefeed
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	104	(*ANYCRLF) any of the three above
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	105	(*ANY) all Unicode newline sequences
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	106	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	107	These override the default and the options given to <b>pcre_compile()</b>. For
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	108	example, on a Unix system where LF is the default newline sequence, the pattern
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	109	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	110	(*CR)a.b
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	111	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	112	changes the convention to CR. That pattern matches "a\nb" because LF is no
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	113	longer a newline. Note that these special settings, which are not
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	114	Perl-compatible, are recognized only at the very start of a pattern, and that
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	115	they must be in upper case. If more than one of them is present, the last one
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	116	is used.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	117	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	118	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	119	The newline convention does not affect what the \R escape sequence matches. By
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	120	default, this is any Unicode newline sequence, for Perl compatibility. However,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	121	this can be changed; see the description of \R in the section entitled
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	122	<a href="#newlineseq">"Newline sequences"</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	123	below. A change of \R setting can be combined with a change of newline
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	124	convention.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	125	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	126	<br><a name="SEC3" href="#TOC1">CHARACTERS AND METACHARACTERS</a><br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	127	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	128	A regular expression is a pattern that is matched against a subject string from
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	129	left to right. Most characters stand for themselves in a pattern, and match the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	130	corresponding characters in the subject. As a trivial example, the pattern
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	131	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	132	The quick brown fox
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	133	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	134	matches a portion of a subject string that is identical to itself. When
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	135	caseless matching is specified (the PCRE_CASELESS option), letters are matched
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	136	independently of case. In UTF-8 mode, PCRE always understands the concept of
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	137	case for characters whose values are less than 128, so caseless matching is
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	138	always possible. For characters with higher values, the concept of case is
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	139	supported if PCRE is compiled with Unicode property support, but not otherwise.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	140	If you want to use caseless matching for characters 128 and above, you must
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	141	ensure that PCRE is compiled with Unicode property support as well as with
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	142	UTF-8 support.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	143	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	144	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	145	The power of regular expressions comes from the ability to include alternatives
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	146	and repetitions in the pattern. These are encoded in the pattern by the use of
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	147	<i>metacharacters</i>, which do not stand for themselves but instead are
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	148	interpreted in some special way.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	149	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	150	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	151	There are two different sets of metacharacters: those that are recognized
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	152	anywhere in the pattern except within square brackets, and those that are
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	153	recognized within square brackets. Outside square brackets, the metacharacters
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	154	are as follows:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	155	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	156	\ general escape character with several uses
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	157	^ assert start of string (or line, in multiline mode)
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	158	$ assert end of string (or line, in multiline mode)
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	159	. match any character except newline (by default)
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	160	[ start character class definition
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	161	\| start of alternative branch
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	162	( start subpattern
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	163	) end subpattern
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	164	? extends the meaning of (
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	165	also 0 or 1 quantifier
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	166	also quantifier minimizer
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	167	* 0 or more quantifier
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	168	+ 1 or more quantifier
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	169	also "possessive quantifier"
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	170	{ start min/max quantifier
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	171	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	172	Part of a pattern that is in square brackets is called a "character class". In
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	173	a character class the only metacharacters are:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	174	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	175	\ general escape character
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	176	^ negate the class, but only if the first character
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	177	- indicates character range
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	178	[ POSIX character class (only if followed by POSIX syntax)
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	179	] terminates the character class
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	180	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	181	The following sections describe the use of each of the metacharacters.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	182	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	183	<br><a name="SEC4" href="#TOC1">BACKSLASH</a><br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	184	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	185	The backslash character has several uses. Firstly, if it is followed by a
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	186	non-alphanumeric character, it takes away any special meaning that character
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	187	may have. This use of backslash as an escape character applies both inside and
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	188	outside character classes.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	189	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	190	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	191	For example, if you want to match a * character, you write \* in the pattern.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	192	This escaping action applies whether or not the following character would
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	193	otherwise be interpreted as a metacharacter, so it is always safe to precede a
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	194	non-alphanumeric with backslash to specify that it stands for itself. In
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	195	particular, if you want to match a backslash, you write \\.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	196	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	197	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	198	If a pattern is compiled with the PCRE_EXTENDED option, whitespace in the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	199	pattern (other than in a character class) and characters between a # outside
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	200	a character class and the next newline are ignored. An escaping backslash can
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	201	be used to include a whitespace or # character as part of the pattern.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	202	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	203	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	204	If you want to remove the special meaning from a sequence of characters, you
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	205	can do so by putting them between \Q and \E. This is different from Perl in
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	206	that $ and @ are handled as literals in \Q...\E sequences in PCRE, whereas in
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	207	Perl, $ and @ cause variable interpolation. Note the following examples:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	208	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	209	Pattern PCRE matches Perl matches
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	210
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	211	\Qabc$xyz\E abc$xyz abc followed by the contents of $xyz
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	212	\Qabc\$xyz\E abc\$xyz abc\$xyz
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	213	\Qabc\E\$\Qxyz\E abc$xyz abc$xyz
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	214	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	215	The \Q...\E sequence is recognized both inside and outside character classes.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	216	<a name="digitsafterbackslash"></a></P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	217	<br><b>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	218	Non-printing characters
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	219	</b><br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	220	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	221	A second use of backslash provides a way of encoding non-printing characters
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	222	in patterns in a visible manner. There is no restriction on the appearance of
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	223	non-printing characters, apart from the binary zero that terminates a pattern,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	224	but when a pattern is being prepared by text editing, it is usually easier to
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	225	use one of the following escape sequences than the binary character it
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	226	represents:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	227	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	228	\a alarm, that is, the BEL character (hex 07)
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	229	\cx "control-x", where x is any character
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	230	\e escape (hex 1B)
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	231	\f formfeed (hex 0C)
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	232	\n linefeed (hex 0A)
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	233	\r carriage return (hex 0D)
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	234	\t tab (hex 09)
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	235	\ddd character with octal code ddd, or backreference
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	236	\xhh character with hex code hh
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	237	\x{hhh..} character with hex code hhh..
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	238	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	239	The precise effect of \cx is as follows: if x is a lower case letter, it
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	240	is converted to upper case. Then bit 6 of the character (hex 40) is inverted.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	241	Thus \cz becomes hex 1A, but \c{ becomes hex 3B, while \c; becomes hex
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	242	7B.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	243	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	244	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	245	After \x, from zero to two hexadecimal digits are read (letters can be in
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	246	upper or lower case). Any number of hexadecimal digits may appear between \x{
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	247	and }, but the value of the character code must be less than 256 in non-UTF-8
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	248	mode, and less than 2**31 in UTF-8 mode. That is, the maximum value in
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	249	hexadecimal is 7FFFFFFF. Note that this is bigger than the largest Unicode code
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	250	point, which is 10FFFF.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	251	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	252	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	253	If characters other than hexadecimal digits appear between \x{ and }, or if
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	254	there is no terminating }, this form of escape is not recognized. Instead, the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	255	initial \x will be interpreted as a basic hexadecimal escape, with no
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	256	following digits, giving a character whose value is zero.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	257	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	258	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	259	Characters whose value is less than 256 can be defined by either of the two
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	260	syntaxes for \x. There is no difference in the way they are handled. For
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	261	example, \xdc is exactly the same as \x{dc}.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	262	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	263	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	264	After \0 up to two further octal digits are read. If there are fewer than two
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	265	digits, just those that are present are used. Thus the sequence \0\x\07
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	266	specifies two binary zeros followed by a BEL character (code value 7). Make
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	267	sure you supply two digits after the initial zero if the pattern character that
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	268	follows is itself an octal digit.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	269	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	270	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	271	The handling of a backslash followed by a digit other than 0 is complicated.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	272	Outside a character class, PCRE reads it and any following digits as a decimal
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	273	number. If the number is less than 10, or if there have been at least that many
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	274	previous capturing left parentheses in the expression, the entire sequence is
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	275	taken as a <i>back reference</i>. A description of how this works is given
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	276	<a href="#backreferences">later,</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	277	following the discussion of
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	278	<a href="#subpattern">parenthesized subpatterns.</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	279	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	280	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	281	Inside a character class, or if the decimal number is greater than 9 and there
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	282	have not been that many capturing subpatterns, PCRE re-reads up to three octal
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	283	digits following the backslash, and uses them to generate a data character. Any
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	284	subsequent digits stand for themselves. In non-UTF-8 mode, the value of a
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	285	character specified in octal must be less than \400. In UTF-8 mode, values up
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	286	to \777 are permitted. For example:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	287	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	288	\040 is another way of writing a space
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	289	\40 is the same, provided there are fewer than 40 previous capturing subpatterns
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	290	\7 is always a back reference
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	291	\11 might be a back reference, or another way of writing a tab
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	292	\011 is always a tab
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	293	\0113 is a tab followed by the character "3"
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	294	\113 might be a back reference, otherwise the character with octal code 113
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	295	\377 might be a back reference, otherwise the byte consisting entirely of 1 bits
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	296	\81 is either a back reference, or a binary zero followed by the two characters "8" and "1"
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	297	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	298	Note that octal values of 100 or greater must not be introduced by a leading
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	299	zero, because no more than three octal digits are ever read.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	300	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	301	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	302	All the sequences that define a single character value can be used both inside
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	303	and outside character classes. In addition, inside a character class, the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	304	sequence \b is interpreted as the backspace character (hex 08), and the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	305	sequences \R and \X are interpreted as the characters "R" and "X",
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	306	respectively. Outside a character class, these sequences have different
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	307	meanings
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	308	<a href="#uniextseq">(see below).</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	309	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	310	<br><b>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	311	Absolute and relative back references
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	312	</b><br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	313	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	314	The sequence \g followed by an unsigned or a negative number, optionally
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	315	enclosed in braces, is an absolute or relative back reference. A named back
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	316	reference can be coded as \g{name}. Back references are discussed
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	317	<a href="#backreferences">later,</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	318	following the discussion of
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	319	<a href="#subpattern">parenthesized subpatterns.</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	320	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	321	<br><b>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	322	Absolute and relative subroutine calls
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	323	</b><br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	324	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	325	For compatibility with Oniguruma, the non-Perl syntax \g followed by a name or
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	326	a number enclosed either in angle brackets or single quotes, is an alternative
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	327	syntax for referencing a subpattern as a "subroutine". Details are discussed
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	328	<a href="#onigurumasubroutines">later.</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	329	Note that \g{...} (Perl syntax) and \g<...> (Oniguruma syntax) are <i>not</i>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	330	synonymous. The former is a back reference; the latter is a subroutine call.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	331	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	332	<br><b>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	333	Generic character types
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	334	</b><br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	335	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	336	Another use of backslash is for specifying generic character types. The
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	337	following are always recognized:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	338	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	339	\d any decimal digit
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	340	\D any character that is not a decimal digit
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	341	\h any horizontal whitespace character
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	342	\H any character that is not a horizontal whitespace character
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	343	\s any whitespace character
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	344	\S any character that is not a whitespace character
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	345	\v any vertical whitespace character
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	346	\V any character that is not a vertical whitespace character
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	347	\w any "word" character
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	348	\W any "non-word" character
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	349	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	350	Each pair of escape sequences partitions the complete set of characters into
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	351	two disjoint sets. Any given character matches one, and only one, of each pair.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	352	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	353	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	354	These character type sequences can appear both inside and outside character
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	355	classes. They each match one character of the appropriate type. If the current
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	356	matching point is at the end of the subject string, all of them fail, since
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	357	there is no character to match.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	358	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	359	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	360	For compatibility with Perl, \s does not match the VT character (code 11).
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	361	This makes it different from the the POSIX "space" class. The \s characters
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	362	are HT (9), LF (10), FF (12), CR (13), and space (32). If "use locale;" is
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	363	included in a Perl script, \s may match the VT character. In PCRE, it never
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	364	does.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	365	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	366	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	367	In UTF-8 mode, characters with values greater than 128 never match \d, \s, or
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	368	\w, and always match \D, \S, and \W. This is true even when Unicode
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	369	character property support is available. These sequences retain their original
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	370	meanings from before UTF-8 support was available, mainly for efficiency
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	371	reasons.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	372	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	373	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	374	The sequences \h, \H, \v, and \V are Perl 5.10 features. In contrast to the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	375	other sequences, these do match certain high-valued codepoints in UTF-8 mode.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	376	The horizontal space characters are:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	377	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	378	U+0009 Horizontal tab
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	379	U+0020 Space
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	380	U+00A0 Non-break space
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	381	U+1680 Ogham space mark
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	382	U+180E Mongolian vowel separator
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	383	U+2000 En quad
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	384	U+2001 Em quad
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	385	U+2002 En space
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	386	U+2003 Em space
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	387	U+2004 Three-per-em space
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	388	U+2005 Four-per-em space
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	389	U+2006 Six-per-em space
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	390	U+2007 Figure space
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	391	U+2008 Punctuation space
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	392	U+2009 Thin space
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	393	U+200A Hair space
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	394	U+202F Narrow no-break space
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	395	U+205F Medium mathematical space
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	396	U+3000 Ideographic space
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	397	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	398	The vertical space characters are:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	399	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	400	U+000A Linefeed
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	401	U+000B Vertical tab
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	402	U+000C Formfeed
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	403	U+000D Carriage return
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	404	U+0085 Next line
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	405	U+2028 Line separator
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	406	U+2029 Paragraph separator
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	407	</PRE>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	408	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	409	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	410	A "word" character is an underscore or any character less than 256 that is a
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	411	letter or digit. The definition of letters and digits is controlled by PCRE's
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	412	low-valued character tables, and may vary if locale-specific matching is taking
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	413	place (see
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	414	<a href="pcreapi.html#localesupport">"Locale support"</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	415	in the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	416	<a href="pcreapi.html"><b>pcreapi</b></a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	417	page). For example, in a French locale such as "fr_FR" in Unix-like systems,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	418	or "french" in Windows, some character codes greater than 128 are used for
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	419	accented letters, and these are matched by \w. The use of locales with Unicode
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	420	is discouraged.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	421	<a name="newlineseq"></a></P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	422	<br><b>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	423	Newline sequences
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	424	</b><br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	425	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	426	Outside a character class, by default, the escape sequence \R matches any
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	427	Unicode newline sequence. This is a Perl 5.10 feature. In non-UTF-8 mode \R is
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	428	equivalent to the following:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	429	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	430	(?>\r\n\|\n\|\x0b\|\f\|\r\|\x85)
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	431	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	432	This is an example of an "atomic group", details of which are given
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	433	<a href="#atomicgroup">below.</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	434	This particular group matches either the two-character sequence CR followed by
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	435	LF, or one of the single characters LF (linefeed, U+000A), VT (vertical tab,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	436	U+000B), FF (formfeed, U+000C), CR (carriage return, U+000D), or NEL (next
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	437	line, U+0085). The two-character sequence is treated as a single unit that
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	438	cannot be split.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	439	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	440	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	441	In UTF-8 mode, two additional characters whose codepoints are greater than 255
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	442	are added: LS (line separator, U+2028) and PS (paragraph separator, U+2029).
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	443	Unicode character property support is not needed for these characters to be
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	444	recognized.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	445	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	446	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	447	It is possible to restrict \R to match only CR, LF, or CRLF (instead of the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	448	complete set of Unicode line endings) by setting the option PCRE_BSR_ANYCRLF
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	449	either at compile time or when the pattern is matched. (BSR is an abbrevation
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	450	for "backslash R".) This can be made the default when PCRE is built; if this is
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	451	the case, the other behaviour can be requested via the PCRE_BSR_UNICODE option.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	452	It is also possible to specify these settings by starting a pattern string with
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	453	one of the following sequences:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	454	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	455	(*BSR_ANYCRLF) CR, LF, or CRLF only
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	456	(*BSR_UNICODE) any Unicode newline sequence
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	457	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	458	These override the default and the options given to <b>pcre_compile()</b>, but
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	459	they can be overridden by options given to <b>pcre_exec()</b>. Note that these
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	460	special settings, which are not Perl-compatible, are recognized only at the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	461	very start of a pattern, and that they must be in upper case. If more than one
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	462	of them is present, the last one is used. They can be combined with a change of
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	463	newline convention, for example, a pattern can start with:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	464	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	465	(ANY)(BSR_ANYCRLF)
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	466	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	467	Inside a character class, \R matches the letter "R".
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	468	<a name="uniextseq"></a></P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	469	<br><b>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	470	Unicode character properties
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	471	</b><br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	472	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	473	When PCRE is built with Unicode character property support, three additional
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	474	escape sequences that match characters with specific properties are available.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	475	When not in UTF-8 mode, these sequences are of course limited to testing
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	476	characters whose codepoints are less than 256, but they do work in this mode.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	477	The extra escape sequences are:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	478	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	479	\p{<i>xx</i>} a character with the <i>xx</i> property
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	480	\P{<i>xx</i>} a character without the <i>xx</i> property
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	481	\X an extended Unicode sequence
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	482	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	483	The property names represented by <i>xx</i> above are limited to the Unicode
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	484	script names, the general category properties, and "Any", which matches any
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	485	character (including newline). Other properties such as "InMusicalSymbols" are
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	486	not currently supported by PCRE. Note that \P{Any} does not match any
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	487	characters, so always causes a match failure.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	488	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	489	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	490	Sets of Unicode characters are defined as belonging to certain scripts. A
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	491	character from one of these sets can be matched using a script name. For
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	492	example:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	493	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	494	\p{Greek}
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	495	\P{Han}
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	496	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	497	Those that are not part of an identified script are lumped together as
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	498	"Common". The current list of scripts is:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	499	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	500	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	501	Arabic,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	502	Armenian,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	503	Balinese,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	504	Bengali,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	505	Bopomofo,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	506	Braille,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	507	Buginese,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	508	Buhid,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	509	Canadian_Aboriginal,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	510	Cherokee,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	511	Common,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	512	Coptic,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	513	Cuneiform,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	514	Cypriot,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	515	Cyrillic,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	516	Deseret,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	517	Devanagari,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	518	Ethiopic,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	519	Georgian,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	520	Glagolitic,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	521	Gothic,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	522	Greek,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	523	Gujarati,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	524	Gurmukhi,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	525	Han,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	526	Hangul,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	527	Hanunoo,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	528	Hebrew,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	529	Hiragana,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	530	Inherited,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	531	Kannada,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	532	Katakana,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	533	Kharoshthi,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	534	Khmer,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	535	Lao,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	536	Latin,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	537	Limbu,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	538	Linear_B,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	539	Malayalam,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	540	Mongolian,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	541	Myanmar,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	542	New_Tai_Lue,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	543	Nko,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	544	Ogham,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	545	Old_Italic,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	546	Old_Persian,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	547	Oriya,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	548	Osmanya,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	549	Phags_Pa,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	550	Phoenician,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	551	Runic,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	552	Shavian,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	553	Sinhala,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	554	Syloti_Nagri,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	555	Syriac,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	556	Tagalog,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	557	Tagbanwa,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	558	Tai_Le,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	559	Tamil,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	560	Telugu,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	561	Thaana,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	562	Thai,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	563	Tibetan,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	564	Tifinagh,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	565	Ugaritic,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	566	Yi.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	567	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	568	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	569	Each character has exactly one general category property, specified by a
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	570	two-letter abbreviation. For compatibility with Perl, negation can be specified
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	571	by including a circumflex between the opening brace and the property name. For
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	572	example, \p{^Lu} is the same as \P{Lu}.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	573	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	574	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	575	If only one letter is specified with \p or \P, it includes all the general
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	576	category properties that start with that letter. In this case, in the absence
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	577	of negation, the curly brackets in the escape sequence are optional; these two
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	578	examples have the same effect:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	579	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	580	\p{L}
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	581	\pL
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	582	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	583	The following general category property codes are supported:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	584	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	585	C Other
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	586	Cc Control
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	587	Cf Format
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	588	Cn Unassigned
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	589	Co Private use
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	590	Cs Surrogate
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	591
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	592	L Letter
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	593	Ll Lower case letter
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	594	Lm Modifier letter
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	595	Lo Other letter
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	596	Lt Title case letter
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	597	Lu Upper case letter
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	598
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	599	M Mark
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	600	Mc Spacing mark
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	601	Me Enclosing mark
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	602	Mn Non-spacing mark
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	603
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	604	N Number
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	605	Nd Decimal number
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	606	Nl Letter number
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	607	No Other number
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	608
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	609	P Punctuation
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	610	Pc Connector punctuation
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	611	Pd Dash punctuation
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	612	Pe Close punctuation
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	613	Pf Final punctuation
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	614	Pi Initial punctuation
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	615	Po Other punctuation
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	616	Ps Open punctuation
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	617
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	618	S Symbol
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	619	Sc Currency symbol
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	620	Sk Modifier symbol
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	621	Sm Mathematical symbol
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	622	So Other symbol
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	623
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	624	Z Separator
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	625	Zl Line separator
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	626	Zp Paragraph separator
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	627	Zs Space separator
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	628	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	629	The special property L& is also supported: it matches a character that has
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	630	the Lu, Ll, or Lt property, in other words, a letter that is not classified as
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	631	a modifier or "other".
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	632	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	633	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	634	The Cs (Surrogate) property applies only to characters in the range U+D800 to
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	635	U+DFFF. Such characters are not valid in UTF-8 strings (see RFC 3629) and so
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	636	cannot be tested by PCRE, unless UTF-8 validity checking has been turned off
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	637	(see the discussion of PCRE_NO_UTF8_CHECK in the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	638	<a href="pcreapi.html"><b>pcreapi</b></a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	639	page).
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	640	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	641	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	642	The long synonyms for these properties that Perl supports (such as \p{Letter})
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	643	are not supported by PCRE, nor is it permitted to prefix any of these
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	644	properties with "Is".
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	645	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	646	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	647	No character that is in the Unicode table has the Cn (unassigned) property.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	648	Instead, this property is assumed for any code point that is not in the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	649	Unicode table.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	650	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	651	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	652	Specifying caseless matching does not affect these escape sequences. For
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	653	example, \p{Lu} always matches only upper case letters.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	654	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	655	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	656	The \X escape matches any number of Unicode characters that form an extended
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	657	Unicode sequence. \X is equivalent to
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	658	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	659	(?>\PM\pM*)
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	660	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	661	That is, it matches a character without the "mark" property, followed by zero
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	662	or more characters with the "mark" property, and treats the sequence as an
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	663	atomic group
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	664	<a href="#atomicgroup">(see below).</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	665	Characters with the "mark" property are typically accents that affect the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	666	preceding character. None of them have codepoints less than 256, so in
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	667	non-UTF-8 mode \X matches any one character.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	668	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	669	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	670	Matching characters by Unicode property is not fast, because PCRE has to search
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	671	a structure that contains data for over fifteen thousand characters. That is
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	672	why the traditional escape sequences such as \d and \w do not use Unicode
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	673	properties in PCRE.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	674	<a name="resetmatchstart"></a></P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	675	<br><b>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	676	Resetting the match start
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	677	</b><br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	678	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	679	The escape sequence \K, which is a Perl 5.10 feature, causes any previously
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	680	matched characters not to be included in the final matched sequence. For
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	681	example, the pattern:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	682	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	683	foo\Kbar
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	684	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	685	matches "foobar", but reports that it has matched "bar". This feature is
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	686	similar to a lookbehind assertion
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	687	<a href="#lookbehind">(described below).</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	688	However, in this case, the part of the subject before the real match does not
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	689	have to be of fixed length, as lookbehind assertions do. The use of \K does
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	690	not interfere with the setting of
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	691	<a href="#subpattern">captured substrings.</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	692	For example, when the pattern
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	693	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	694	(foo)\Kbar
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	695	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	696	matches "foobar", the first substring is still set to "foo".
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	697	<a name="smallassertions"></a></P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	698	<br><b>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	699	Simple assertions
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	700	</b><br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	701	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	702	The final use of backslash is for certain simple assertions. An assertion
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	703	specifies a condition that has to be met at a particular point in a match,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	704	without consuming any characters from the subject string. The use of
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	705	subpatterns for more complicated assertions is described
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	706	<a href="#bigassertions">below.</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	707	The backslashed assertions are:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	708	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	709	\b matches at a word boundary
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	710	\B matches when not at a word boundary
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	711	\A matches at the start of the subject
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	712	\Z matches at the end of the subject
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	713	also matches before a newline at the end of the subject
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	714	\z matches only at the end of the subject
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	715	\G matches at the first matching position in the subject
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	716	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	717	These assertions may not appear in character classes (but note that \b has a
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	718	different meaning, namely the backspace character, inside a character class).
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	719	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	720	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	721	A word boundary is a position in the subject string where the current character
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	722	and the previous character do not both match \w or \W (i.e. one matches
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	723	\w and the other matches \W), or the start or end of the string if the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	724	first or last character matches \w, respectively.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	725	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	726	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	727	The \A, \Z, and \z assertions differ from the traditional circumflex and
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	728	dollar (described in the next section) in that they only ever match at the very
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	729	start and end of the subject string, whatever options are set. Thus, they are
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	730	independent of multiline mode. These three assertions are not affected by the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	731	PCRE_NOTBOL or PCRE_NOTEOL options, which affect only the behaviour of the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	732	circumflex and dollar metacharacters. However, if the <i>startoffset</i>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	733	argument of <b>pcre_exec()</b> is non-zero, indicating that matching is to start
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	734	at a point other than the beginning of the subject, \A can never match. The
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	735	difference between \Z and \z is that \Z matches before a newline at the end
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	736	of the string as well as at the very end, whereas \z matches only at the end.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	737	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	738	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	739	The \G assertion is true only when the current matching position is at the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	740	start point of the match, as specified by the <i>startoffset</i> argument of
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	741	<b>pcre_exec()</b>. It differs from \A when the value of <i>startoffset</i> is
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	742	non-zero. By calling <b>pcre_exec()</b> multiple times with appropriate
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	743	arguments, you can mimic Perl's /g option, and it is in this kind of
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	744	implementation where \G can be useful.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	745	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	746	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	747	Note, however, that PCRE's interpretation of \G, as the start of the current
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	748	match, is subtly different from Perl's, which defines it as the end of the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	749	previous match. In Perl, these can be different when the previously matched
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	750	string was empty. Because PCRE does just one match at a time, it cannot
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	751	reproduce this behaviour.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	752	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	753	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	754	If all the alternatives of a pattern begin with \G, the expression is anchored
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	755	to the starting match position, and the "anchored" flag is set in the compiled
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	756	regular expression.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	757	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	758	<br><a name="SEC5" href="#TOC1">CIRCUMFLEX AND DOLLAR</a><br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	759	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	760	Outside a character class, in the default matching mode, the circumflex
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	761	character is an assertion that is true only if the current matching point is
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	762	at the start of the subject string. If the <i>startoffset</i> argument of
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	763	<b>pcre_exec()</b> is non-zero, circumflex can never match if the PCRE_MULTILINE
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	764	option is unset. Inside a character class, circumflex has an entirely different
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	765	meaning
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	766	<a href="#characterclass">(see below).</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	767	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	768	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	769	Circumflex need not be the first character of the pattern if a number of
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	770	alternatives are involved, but it should be the first thing in each alternative
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	771	in which it appears if the pattern is ever to match that branch. If all
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	772	possible alternatives start with a circumflex, that is, if the pattern is
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	773	constrained to match only at the start of the subject, it is said to be an
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	774	"anchored" pattern. (There are also other constructs that can cause a pattern
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	775	to be anchored.)
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	776	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	777	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	778	A dollar character is an assertion that is true only if the current matching
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	779	point is at the end of the subject string, or immediately before a newline
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	780	at the end of the string (by default). Dollar need not be the last character of
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	781	the pattern if a number of alternatives are involved, but it should be the last
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	782	item in any branch in which it appears. Dollar has no special meaning in a
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	783	character class.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	784	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	785	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	786	The meaning of dollar can be changed so that it matches only at the very end of
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	787	the string, by setting the PCRE_DOLLAR_ENDONLY option at compile time. This
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	788	does not affect the \Z assertion.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	789	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	790	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	791	The meanings of the circumflex and dollar characters are changed if the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	792	PCRE_MULTILINE option is set. When this is the case, a circumflex matches
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	793	immediately after internal newlines as well as at the start of the subject
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	794	string. It does not match after a newline that ends the string. A dollar
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	795	matches before any newlines in the string, as well as at the very end, when
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	796	PCRE_MULTILINE is set. When newline is specified as the two-character
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	797	sequence CRLF, isolated CR and LF characters do not indicate newlines.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	798	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	799	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	800	For example, the pattern /^abc$/ matches the subject string "def\nabc" (where
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	801	\n represents a newline) in multiline mode, but not otherwise. Consequently,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	802	patterns that are anchored in single line mode because all branches start with
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	803	^ are not anchored in multiline mode, and a match for circumflex is possible
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	804	when the <i>startoffset</i> argument of <b>pcre_exec()</b> is non-zero. The
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	805	PCRE_DOLLAR_ENDONLY option is ignored if PCRE_MULTILINE is set.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	806	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	807	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	808	Note that the sequences \A, \Z, and \z can be used to match the start and
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	809	end of the subject in both modes, and if all branches of a pattern start with
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	810	\A it is always anchored, whether or not PCRE_MULTILINE is set.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	811	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	812	<br><a name="SEC6" href="#TOC1">FULL STOP (PERIOD, DOT)</a><br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	813	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	814	Outside a character class, a dot in the pattern matches any one character in
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	815	the subject string except (by default) a character that signifies the end of a
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	816	line. In UTF-8 mode, the matched character may be more than one byte long.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	817	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	818	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	819	When a line ending is defined as a single character, dot never matches that
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	820	character; when the two-character sequence CRLF is used, dot does not match CR
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	821	if it is immediately followed by LF, but otherwise it matches all characters
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	822	(including isolated CRs and LFs). When any Unicode line endings are being
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	823	recognized, dot does not match CR or LF or any of the other line ending
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	824	characters.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	825	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	826	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	827	The behaviour of dot with regard to newlines can be changed. If the PCRE_DOTALL
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	828	option is set, a dot matches any one character, without exception. If the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	829	two-character sequence CRLF is present in the subject string, it takes two dots
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	830	to match it.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	831	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	832	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	833	The handling of dot is entirely independent of the handling of circumflex and
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	834	dollar, the only relationship being that they both involve newlines. Dot has no
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	835	special meaning in a character class.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	836	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	837	<br><a name="SEC7" href="#TOC1">MATCHING A SINGLE BYTE</a><br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	838	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	839	Outside a character class, the escape sequence \C matches any one byte, both
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	840	in and out of UTF-8 mode. Unlike a dot, it always matches any line-ending
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	841	characters. The feature is provided in Perl in order to match individual bytes
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	842	in UTF-8 mode. Because it breaks up UTF-8 characters into individual bytes,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	843	what remains in the string may be a malformed UTF-8 string. For this reason,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	844	the \C escape sequence is best avoided.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	845	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	846	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	847	PCRE does not allow \C to appear in lookbehind assertions
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	848	<a href="#lookbehind">(described below),</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	849	because in UTF-8 mode this would make it impossible to calculate the length of
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	850	the lookbehind.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	851	<a name="characterclass"></a></P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	852	<br><a name="SEC8" href="#TOC1">SQUARE BRACKETS AND CHARACTER CLASSES</a><br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	853	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	854	An opening square bracket introduces a character class, terminated by a closing
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	855	square bracket. A closing square bracket on its own is not special. If a
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	856	closing square bracket is required as a member of the class, it should be the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	857	first data character in the class (after an initial circumflex, if present) or
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	858	escaped with a backslash.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	859	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	860	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	861	A character class matches a single character in the subject. In UTF-8 mode, the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	862	character may occupy more than one byte. A matched character must be in the set
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	863	of characters defined by the class, unless the first character in the class
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	864	definition is a circumflex, in which case the subject character must not be in
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	865	the set defined by the class. If a circumflex is actually required as a member
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	866	of the class, ensure it is not the first character, or escape it with a
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	867	backslash.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	868	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	869	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	870	For example, the character class [aeiou] matches any lower case vowel, while
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	871	[^aeiou] matches any character that is not a lower case vowel. Note that a
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	872	circumflex is just a convenient notation for specifying the characters that
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	873	are in the class by enumerating those that are not. A class that starts with a
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	874	circumflex is not an assertion: it still consumes a character from the subject
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	875	string, and therefore it fails if the current pointer is at the end of the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	876	string.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	877	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	878	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	879	In UTF-8 mode, characters with values greater than 255 can be included in a
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	880	class as a literal string of bytes, or by using the \x{ escaping mechanism.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	881	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	882	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	883	When caseless matching is set, any letters in a class represent both their
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	884	upper case and lower case versions, so for example, a caseless [aeiou] matches
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	885	"A" as well as "a", and a caseless [^aeiou] does not match "A", whereas a
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	886	caseful version would. In UTF-8 mode, PCRE always understands the concept of
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	887	case for characters whose values are less than 128, so caseless matching is
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	888	always possible. For characters with higher values, the concept of case is
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	889	supported if PCRE is compiled with Unicode property support, but not otherwise.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	890	If you want to use caseless matching for characters 128 and above, you must
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	891	ensure that PCRE is compiled with Unicode property support as well as with
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	892	UTF-8 support.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	893	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	894	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	895	Characters that might indicate line breaks are never treated in any special way
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	896	when matching character classes, whatever line-ending sequence is in use, and
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	897	whatever setting of the PCRE_DOTALL and PCRE_MULTILINE options is used. A class
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	898	such as [^a] always matches one of these characters.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	899	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	900	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	901	The minus (hyphen) character can be used to specify a range of characters in a
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	902	character class. For example, [d-m] matches any letter between d and m,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	903	inclusive. If a minus character is required in a class, it must be escaped with
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	904	a backslash or appear in a position where it cannot be interpreted as
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	905	indicating a range, typically as the first or last character in the class.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	906	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	907	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	908	It is not possible to have the literal character "]" as the end character of a
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	909	range. A pattern such as [W-]46] is interpreted as a class of two characters
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	910	("W" and "-") followed by a literal string "46]", so it would match "W46]" or
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	911	"-46]". However, if the "]" is escaped with a backslash it is interpreted as
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	912	the end of range, so [W-\]46] is interpreted as a class containing a range
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	913	followed by two other characters. The octal or hexadecimal representation of
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	914	"]" can also be used to end a range.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	915	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	916	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	917	Ranges operate in the collating sequence of character values. They can also be
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	918	used for characters specified numerically, for example [\000-\037]. In UTF-8
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	919	mode, ranges can include characters whose values are greater than 255, for
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	920	example [\x{100}-\x{2ff}].
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	921	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	922	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	923	If a range that includes letters is used when caseless matching is set, it
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	924	matches the letters in either case. For example, [W-c] is equivalent to
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	925	[][\\^_`wxyzabc], matched caselessly, and in non-UTF-8 mode, if character
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	926	tables for a French locale are in use, [\xc8-\xcb] matches accented E
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	927	characters in both cases. In UTF-8 mode, PCRE supports the concept of case for
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	928	characters with values greater than 128 only when it is compiled with Unicode
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	929	property support.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	930	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	931	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	932	The character types \d, \D, \p, \P, \s, \S, \w, and \W may also appear
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	933	in a character class, and add the characters that they match to the class. For
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	934	example, [\dABCDEF] matches any hexadecimal digit. A circumflex can
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	935	conveniently be used with the upper case character types to specify a more
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	936	restricted set of characters than the matching lower case type. For example,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	937	the class [^\W_] matches any letter or digit, but not underscore.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	938	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	939	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	940	The only metacharacters that are recognized in character classes are backslash,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	941	hyphen (only where it can be interpreted as specifying a range), circumflex
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	942	(only at the start), opening square bracket (only when it can be interpreted as
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	943	introducing a POSIX class name - see the next section), and the terminating
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	944	closing square bracket. However, escaping other non-alphanumeric characters
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	945	does no harm.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	946	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	947	<br><a name="SEC9" href="#TOC1">POSIX CHARACTER CLASSES</a><br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	948	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	949	Perl supports the POSIX notation for character classes. This uses names
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	950	enclosed by [: and :] within the enclosing square brackets. PCRE also supports
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	951	this notation. For example,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	952	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	953	[01[:alpha:]%]
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	954	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	955	matches "0", "1", any alphabetic character, or "%". The supported class names
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	956	are
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	957	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	958	alnum letters and digits
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	959	alpha letters
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	960	ascii character codes 0 - 127
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	961	blank space or tab only
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	962	cntrl control characters
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	963	digit decimal digits (same as \d)
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	964	graph printing characters, excluding space
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	965	lower lower case letters
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	966	print printing characters, including space
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	967	punct printing characters, excluding letters and digits
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	968	space white space (not quite the same as \s)
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	969	upper upper case letters
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	970	word "word" characters (same as \w)
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	971	xdigit hexadecimal digits
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	972	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	973	The "space" characters are HT (9), LF (10), VT (11), FF (12), CR (13), and
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	974	space (32). Notice that this list includes the VT character (code 11). This
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	975	makes "space" different to \s, which does not include VT (for Perl
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	976	compatibility).
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	977	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	978	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	979	The name "word" is a Perl extension, and "blank" is a GNU extension from Perl
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	980	5.8. Another Perl extension is negation, which is indicated by a ^ character
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	981	after the colon. For example,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	982	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	983	[12[:^digit:]]
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	984	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	985	matches "1", "2", or any non-digit. PCRE (and Perl) also recognize the POSIX
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	986	syntax [.ch.] and [=ch=] where "ch" is a "collating element", but these are not
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	987	supported, and an error is given if they are encountered.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	988	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	989	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	990	In UTF-8 mode, characters with values greater than 128 do not match any of
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	991	the POSIX character classes.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	992	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	993	<br><a name="SEC10" href="#TOC1">VERTICAL BAR</a><br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	994	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	995	Vertical bar characters are used to separate alternative patterns. For example,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	996	the pattern
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	997	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	998	gilbert\|sullivan
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	999	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1000	matches either "gilbert" or "sullivan". Any number of alternatives may appear,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1001	and an empty alternative is permitted (matching the empty string). The matching
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1002	process tries each alternative in turn, from left to right, and the first one
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1003	that succeeds is used. If the alternatives are within a subpattern
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1004	<a href="#subpattern">(defined below),</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1005	"succeeds" means matching the rest of the main pattern as well as the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1006	alternative in the subpattern.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1007	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1008	<br><a name="SEC11" href="#TOC1">INTERNAL OPTION SETTING</a><br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1009	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1010	The settings of the PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1011	PCRE_EXTENDED options (which are Perl-compatible) can be changed from within
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1012	the pattern by a sequence of Perl option letters enclosed between "(?" and ")".
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1013	The option letters are
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1014	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1015	i for PCRE_CASELESS
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1016	m for PCRE_MULTILINE
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1017	s for PCRE_DOTALL
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1018	x for PCRE_EXTENDED
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1019	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1020	For example, (?im) sets caseless, multiline matching. It is also possible to
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1021	unset these options by preceding the letter with a hyphen, and a combined
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1022	setting and unsetting such as (?im-sx), which sets PCRE_CASELESS and
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1023	PCRE_MULTILINE while unsetting PCRE_DOTALL and PCRE_EXTENDED, is also
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1024	permitted. If a letter appears both before and after the hyphen, the option is
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1025	unset.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1026	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1027	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1028	The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and PCRE_EXTRA can be
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1029	changed in the same way as the Perl-compatible options by using the characters
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1030	J, U and X respectively.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1031	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1032	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1033	When an option change occurs at top level (that is, not inside subpattern
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1034	parentheses), the change applies to the remainder of the pattern that follows.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1035	If the change is placed right at the start of a pattern, PCRE extracts it into
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1036	the global options (and it will therefore show up in data extracted by the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1037	<b>pcre_fullinfo()</b> function).
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1038	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1039	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1040	An option change within a subpattern (see below for a description of
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1041	subpatterns) affects only that part of the current pattern that follows it, so
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1042	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1043	(a(?i)b)c
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1044	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1045	matches abc and aBc and no other strings (assuming PCRE_CASELESS is not used).
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1046	By this means, options can be made to have different settings in different
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1047	parts of the pattern. Any changes made in one alternative do carry on
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1048	into subsequent branches within the same subpattern. For example,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1049	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1050	(a(?i)b\|c)
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1051	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1052	matches "ab", "aB", "c", and "C", even though when matching "C" the first
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1053	branch is abandoned before the option setting. This is because the effects of
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1054	option settings happen at compile time. There would be some very weird
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1055	behaviour otherwise.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1056	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1057	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1058	<b>Note:</b> There are other PCRE-specific options that can be set by the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1059	application when the compile or match functions are called. In some cases the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1060	pattern can contain special leading sequences to override what the application
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1061	has set or what has been defaulted. Details are given in the section entitled
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1062	<a href="#newlineseq">"Newline sequences"</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1063	above.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1064	<a name="subpattern"></a></P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1065	<br><a name="SEC12" href="#TOC1">SUBPATTERNS</a><br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1066	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1067	Subpatterns are delimited by parentheses (round brackets), which can be nested.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1068	Turning part of a pattern into a subpattern does two things:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1069	<br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1070	<br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1071	1. It localizes a set of alternatives. For example, the pattern
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1072	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1073	cat(aract\|erpillar\|)
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1074	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1075	matches one of the words "cat", "cataract", or "caterpillar". Without the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1076	parentheses, it would match "cataract", "erpillar" or an empty string.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1077	<br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1078	<br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1079	2. It sets up the subpattern as a capturing subpattern. This means that, when
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1080	the whole pattern matches, that portion of the subject string that matched the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1081	subpattern is passed back to the caller via the <i>ovector</i> argument of
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1082	<b>pcre_exec()</b>. Opening parentheses are counted from left to right (starting
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1083	from 1) to obtain numbers for the capturing subpatterns.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1084	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1085	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1086	For example, if the string "the red king" is matched against the pattern
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1087	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1088	the ((red\|white) (king\|queen))
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1089	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1090	the captured substrings are "red king", "red", and "king", and are numbered 1,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1091	2, and 3, respectively.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1092	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1093	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1094	The fact that plain parentheses fulfil two functions is not always helpful.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1095	There are often times when a grouping subpattern is required without a
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1096	capturing requirement. If an opening parenthesis is followed by a question mark
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1097	and a colon, the subpattern does not do any capturing, and is not counted when
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1098	computing the number of any subsequent capturing subpatterns. For example, if
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1099	the string "the white queen" is matched against the pattern
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1100	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1101	the ((?:red\|white) (king\|queen))
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1102	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1103	the captured substrings are "white queen" and "queen", and are numbered 1 and
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1104	2. The maximum number of capturing subpatterns is 65535.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1105	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1106	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1107	As a convenient shorthand, if any option settings are required at the start of
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1108	a non-capturing subpattern, the option letters may appear between the "?" and
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1109	the ":". Thus the two patterns
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1110	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1111	(?i:saturday\|sunday)
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1112	(?:(?i)saturday\|sunday)
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1113	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1114	match exactly the same set of strings. Because alternative branches are tried
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1115	from left to right, and options are not reset until the end of the subpattern
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1116	is reached, an option setting in one branch does affect subsequent branches, so
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1117	the above patterns match "SUNDAY" as well as "Saturday".
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1118	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1119	<br><a name="SEC13" href="#TOC1">DUPLICATE SUBPATTERN NUMBERS</a><br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1120	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1121	Perl 5.10 introduced a feature whereby each alternative in a subpattern uses
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1122	the same numbers for its capturing parentheses. Such a subpattern starts with
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1123	(?\| and is itself a non-capturing subpattern. For example, consider this
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1124	pattern:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1125	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1126	(?\|(Sat)ur\|(Sun))day
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1127	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1128	Because the two alternatives are inside a (?\| group, both sets of capturing
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1129	parentheses are numbered one. Thus, when the pattern matches, you can look
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1130	at captured substring number one, whichever alternative matched. This construct
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1131	is useful when you want to capture part, but not all, of one of a number of
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1132	alternatives. Inside a (?\| group, parentheses are numbered as usual, but the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1133	number is reset at the start of each branch. The numbers of any capturing
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1134	buffers that follow the subpattern start after the highest number used in any
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1135	branch. The following example is taken from the Perl documentation.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1136	The numbers underneath show in which buffer the captured content will be
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1137	stored.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1138	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1139	# before ---------------branch-reset----------- after
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1140	/ ( a ) (?\| x ( y ) z \| (p (q) r) \| (t) u (v) ) ( z ) /x
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1141	# 1 2 2 3 2 3 4
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1142	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1143	A backreference or a recursive call to a numbered subpattern always refers to
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1144	the first one in the pattern with the given number.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1145	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1146	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1147	An alternative approach to using this "branch reset" feature is to use
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1148	duplicate named subpatterns, as described in the next section.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1149	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1150	<br><a name="SEC14" href="#TOC1">NAMED SUBPATTERNS</a><br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1151	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1152	Identifying capturing parentheses by number is simple, but it can be very hard
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1153	to keep track of the numbers in complicated regular expressions. Furthermore,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1154	if an expression is modified, the numbers may change. To help with this
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1155	difficulty, PCRE supports the naming of subpatterns. This feature was not
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1156	added to Perl until release 5.10. Python had the feature earlier, and PCRE
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1157	introduced it at release 4.0, using the Python syntax. PCRE now supports both
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1158	the Perl and the Python syntax.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1159	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1160	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1161	In PCRE, a subpattern can be named in one of three ways: (?<name>...) or
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1162	(?'name'...) as in Perl, or (?P<name>...) as in Python. References to capturing
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1163	parentheses from other parts of the pattern, such as
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1164	<a href="#backreferences">backreferences,</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1165	<a href="#recursion">recursion,</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1166	and
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1167	<a href="#conditions">conditions,</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1168	can be made by name as well as by number.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1169	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1170	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1171	Names consist of up to 32 alphanumeric characters and underscores. Named
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1172	capturing parentheses are still allocated numbers as well as names, exactly as
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1173	if the names were not present. The PCRE API provides function calls for
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1174	extracting the name-to-number translation table from a compiled pattern. There
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1175	is also a convenience function for extracting a captured substring by name.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1176	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1177	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1178	By default, a name must be unique within a pattern, but it is possible to relax
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1179	this constraint by setting the PCRE_DUPNAMES option at compile time. This can
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1180	be useful for patterns where only one instance of the named parentheses can
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1181	match. Suppose you want to match the name of a weekday, either as a 3-letter
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1182	abbreviation or as the full name, and in both cases you want to extract the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1183	abbreviation. This pattern (ignoring the line breaks) does the job:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1184	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1185	(?<DN>Mon\|Fri\|Sun)(?:day)?\|
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1186	(?<DN>Tue)(?:sday)?\|
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1187	(?<DN>Wed)(?:nesday)?\|
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1188	(?<DN>Thu)(?:rsday)?\|
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1189	(?<DN>Sat)(?:urday)?
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1190	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1191	There are five capturing substrings, but only one is ever set after a match.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1192	(An alternative way of solving this problem is to use a "branch reset"
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1193	subpattern, as described in the previous section.)
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1194	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1195	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1196	The convenience function for extracting the data by name returns the substring
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1197	for the first (and in this example, the only) subpattern of that name that
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1198	matched. This saves searching to find which numbered subpattern it was. If you
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1199	make a reference to a non-unique named subpattern from elsewhere in the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1200	pattern, the one that corresponds to the lowest number is used. For further
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1201	details of the interfaces for handling named subpatterns, see the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1202	<a href="pcreapi.html"><b>pcreapi</b></a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1203	documentation.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1204	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1205	<br><a name="SEC15" href="#TOC1">REPETITION</a><br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1206	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1207	Repetition is specified by quantifiers, which can follow any of the following
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1208	items:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1209	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1210	a literal data character
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1211	the dot metacharacter
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1212	the \C escape sequence
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1213	the \X escape sequence (in UTF-8 mode with Unicode properties)
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1214	the \R escape sequence
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1215	an escape such as \d that matches a single character
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1216	a character class
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1217	a back reference (see next section)
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1218	a parenthesized subpattern (unless it is an assertion)
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1219	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1220	The general repetition quantifier specifies a minimum and maximum number of
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1221	permitted matches, by giving the two numbers in curly brackets (braces),
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1222	separated by a comma. The numbers must be less than 65536, and the first must
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1223	be less than or equal to the second. For example:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1224	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1225	z{2,4}
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1226	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1227	matches "zz", "zzz", or "zzzz". A closing brace on its own is not a special
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1228	character. If the second number is omitted, but the comma is present, there is
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1229	no upper limit; if the second number and the comma are both omitted, the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1230	quantifier specifies an exact number of required matches. Thus
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1231	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1232	[aeiou]{3,}
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1233	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1234	matches at least 3 successive vowels, but may match many more, while
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1235	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1236	\d{8}
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1237	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1238	matches exactly 8 digits. An opening curly bracket that appears in a position
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1239	where a quantifier is not allowed, or one that does not match the syntax of a
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1240	quantifier, is taken as a literal character. For example, {,6} is not a
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1241	quantifier, but a literal string of four characters.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1242	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1243	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1244	In UTF-8 mode, quantifiers apply to UTF-8 characters rather than to individual
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1245	bytes. Thus, for example, \x{100}{2} matches two UTF-8 characters, each of
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1246	which is represented by a two-byte sequence. Similarly, when Unicode property
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1247	support is available, \X{3} matches three Unicode extended sequences, each of
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1248	which may be several bytes long (and they may be of different lengths).
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1249	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1250	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1251	The quantifier {0} is permitted, causing the expression to behave as if the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1252	previous item and the quantifier were not present. This may be useful for
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1253	subpatterns that are referenced as
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1254	<a href="#subpatternsassubroutines">subroutines</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1255	from elsewhere in the pattern. Items other than subpatterns that have a {0}
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1256	quantifier are omitted from the compiled pattern.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1257	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1258	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1259	For convenience, the three most common quantifiers have single-character
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1260	abbreviations:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1261	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1262	* is equivalent to {0,}
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1263	+ is equivalent to {1,}
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1264	? is equivalent to {0,1}
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1265	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1266	It is possible to construct infinite loops by following a subpattern that can
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1267	match no characters with a quantifier that has no upper limit, for example:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1268	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1269	(a?)*
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1270	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1271	Earlier versions of Perl and PCRE used to give an error at compile time for
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1272	such patterns. However, because there are cases where this can be useful, such
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1273	patterns are now accepted, but if any repetition of the subpattern does in fact
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1274	match no characters, the loop is forcibly broken.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1275	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1276	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1277	By default, the quantifiers are "greedy", that is, they match as much as
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1278	possible (up to the maximum number of permitted times), without causing the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1279	rest of the pattern to fail. The classic example of where this gives problems
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1280	is in trying to match comments in C programs. These appear between /* and */
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1281	and within the comment, individual * and / characters may appear. An attempt to
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1282	match C comments by applying the pattern
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1283	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1284	/\.\*/
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1285	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1286	to the string
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1287	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1288	/* first comment / not comment / second comment */
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1289	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1290	fails, because it matches the entire string owing to the greediness of the .*
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1291	item.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1292	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1293	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1294	However, if a quantifier is followed by a question mark, it ceases to be
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1295	greedy, and instead matches the minimum number of times possible, so the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1296	pattern
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1297	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1298	/\.?\*/
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1299	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1300	does the right thing with the C comments. The meaning of the various
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1301	quantifiers is not otherwise changed, just the preferred number of matches.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1302	Do not confuse this use of question mark with its use as a quantifier in its
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1303	own right. Because it has two uses, it can sometimes appear doubled, as in
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1304	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1305	\d??\d
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1306	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1307	which matches one digit by preference, but can match two if that is the only
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1308	way the rest of the pattern matches.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1309	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1310	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1311	If the PCRE_UNGREEDY option is set (an option that is not available in Perl),
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1312	the quantifiers are not greedy by default, but individual ones can be made
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1313	greedy by following them with a question mark. In other words, it inverts the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1314	default behaviour.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1315	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1316	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1317	When a parenthesized subpattern is quantified with a minimum repeat count that
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1318	is greater than 1 or with a limited maximum, more memory is required for the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1319	compiled pattern, in proportion to the size of the minimum or maximum.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1320	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1321	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1322	If a pattern starts with .* or .{0,} and the PCRE_DOTALL option (equivalent
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1323	to Perl's /s) is set, thus allowing the dot to match newlines, the pattern is
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1324	implicitly anchored, because whatever follows will be tried against every
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1325	character position in the subject string, so there is no point in retrying the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1326	overall match at any position after the first. PCRE normally treats such a
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1327	pattern as though it were preceded by \A.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1328	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1329	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1330	In cases where it is known that the subject string contains no newlines, it is
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1331	worth setting PCRE_DOTALL in order to obtain this optimization, or
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1332	alternatively using ^ to indicate anchoring explicitly.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1333	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1334	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1335	However, there is one situation where the optimization cannot be used. When .*
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1336	is inside capturing parentheses that are the subject of a backreference
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1337	elsewhere in the pattern, a match at the start may fail where a later one
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1338	succeeds. Consider, for example:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1339	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1340	(.*)abc\1
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1341	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1342	If the subject is "xyz123abc123" the match point is the fourth character. For
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1343	this reason, such a pattern is not implicitly anchored.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1344	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1345	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1346	When a capturing subpattern is repeated, the value captured is the substring
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1347	that matched the final iteration. For example, after
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1348	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1349	(tweedle[dume]{3}\s*)+
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1350	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1351	has matched "tweedledum tweedledee" the value of the captured substring is
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1352	"tweedledee". However, if there are nested capturing subpatterns, the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1353	corresponding captured values may have been set in previous iterations. For
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1354	example, after
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1355	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1356	/(a\|(b))+/
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1357	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1358	matches "aba" the value of the second captured substring is "b".
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1359	<a name="atomicgroup"></a></P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1360	<br><a name="SEC16" href="#TOC1">ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS</a><br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1361	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1362	With both maximizing ("greedy") and minimizing ("ungreedy" or "lazy")
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1363	repetition, failure of what follows normally causes the repeated item to be
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1364	re-evaluated to see if a different number of repeats allows the rest of the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1365	pattern to match. Sometimes it is useful to prevent this, either to change the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1366	nature of the match, or to cause it fail earlier than it otherwise might, when
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1367	the author of the pattern knows there is no point in carrying on.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1368	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1369	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1370	Consider, for example, the pattern \d+foo when applied to the subject line
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1371	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1372	123456bar
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1373	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1374	After matching all 6 digits and then failing to match "foo", the normal
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1375	action of the matcher is to try again with only 5 digits matching the \d+
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1376	item, and then with 4, and so on, before ultimately failing. "Atomic grouping"
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1377	(a term taken from Jeffrey Friedl's book) provides the means for specifying
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1378	that once a subpattern has matched, it is not to be re-evaluated in this way.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1379	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1380	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1381	If we use atomic grouping for the previous example, the matcher gives up
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1382	immediately on failing to match "foo" the first time. The notation is a kind of
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1383	special parenthesis, starting with (?> as in this example:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1384	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1385	(?>\d+)foo
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1386	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1387	This kind of parenthesis "locks up" the part of the pattern it contains once
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1388	it has matched, and a failure further into the pattern is prevented from
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1389	backtracking into it. Backtracking past it to previous items, however, works as
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1390	normal.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1391	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1392	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1393	An alternative description is that a subpattern of this type matches the string
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1394	of characters that an identical standalone pattern would match, if anchored at
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1395	the current point in the subject string.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1396	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1397	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1398	Atomic grouping subpatterns are not capturing subpatterns. Simple cases such as
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1399	the above example can be thought of as a maximizing repeat that must swallow
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1400	everything it can. So, while both \d+ and \d+? are prepared to adjust the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1401	number of digits they match in order to make the rest of the pattern match,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1402	(?>\d+) can only match an entire sequence of digits.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1403	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1404	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1405	Atomic groups in general can of course contain arbitrarily complicated
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1406	subpatterns, and can be nested. However, when the subpattern for an atomic
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1407	group is just a single repeated item, as in the example above, a simpler
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1408	notation, called a "possessive quantifier" can be used. This consists of an
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1409	additional + character following a quantifier. Using this notation, the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1410	previous example can be rewritten as
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1411	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1412	\d++foo
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1413	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1414	Note that a possessive quantifier can be used with an entire group, for
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1415	example:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1416	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1417	(abc\|xyz){2,3}+
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1418	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1419	Possessive quantifiers are always greedy; the setting of the PCRE_UNGREEDY
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1420	option is ignored. They are a convenient notation for the simpler forms of
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1421	atomic group. However, there is no difference in the meaning of a possessive
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1422	quantifier and the equivalent atomic group, though there may be a performance
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1423	difference; possessive quantifiers should be slightly faster.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1424	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1425	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1426	The possessive quantifier syntax is an extension to the Perl 5.8 syntax.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1427	Jeffrey Friedl originated the idea (and the name) in the first edition of his
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1428	book. Mike McCloskey liked it, so implemented it when he built Sun's Java
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1429	package, and PCRE copied it from there. It ultimately found its way into Perl
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1430	at release 5.10.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1431	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1432	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1433	PCRE has an optimization that automatically "possessifies" certain simple
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1434	pattern constructs. For example, the sequence A+B is treated as A++B because
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1435	there is no point in backtracking into a sequence of A's when B must follow.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1436	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1437	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1438	When a pattern contains an unlimited repeat inside a subpattern that can itself
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1439	be repeated an unlimited number of times, the use of an atomic group is the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1440	only way to avoid some failing matches taking a very long time indeed. The
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1441	pattern
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1442	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1443	(\D+\|<\d+>)*[!?]
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1444	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1445	matches an unlimited number of substrings that either consist of non-digits, or
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1446	digits enclosed in <>, followed by either ! or ?. When it matches, it runs
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1447	quickly. However, if it is applied to
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1448	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1449	aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1450	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1451	it takes a long time before reporting failure. This is because the string can
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1452	be divided between the internal \D+ repeat and the external * repeat in a
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1453	large number of ways, and all have to be tried. (The example uses [!?] rather
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1454	than a single character at the end, because both PCRE and Perl have an
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1455	optimization that allows for fast failure when a single character is used. They
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1456	remember the last single character that is required for a match, and fail early
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1457	if it is not present in the string.) If the pattern is changed so that it uses
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1458	an atomic group, like this:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1459	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1460	((?>\D+)\|<\d+>)*[!?]
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1461	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1462	sequences of non-digits cannot be broken, and failure happens quickly.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1463	<a name="backreferences"></a></P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1464	<br><a name="SEC17" href="#TOC1">BACK REFERENCES</a><br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1465	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1466	Outside a character class, a backslash followed by a digit greater than 0 (and
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1467	possibly further digits) is a back reference to a capturing subpattern earlier
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1468	(that is, to its left) in the pattern, provided there have been that many
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1469	previous capturing left parentheses.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1470	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1471	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1472	However, if the decimal number following the backslash is less than 10, it is
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1473	always taken as a back reference, and causes an error only if there are not
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1474	that many capturing left parentheses in the entire pattern. In other words, the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1475	parentheses that are referenced need not be to the left of the reference for
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1476	numbers less than 10. A "forward back reference" of this type can make sense
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1477	when a repetition is involved and the subpattern to the right has participated
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1478	in an earlier iteration.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1479	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1480	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1481	It is not possible to have a numerical "forward back reference" to a subpattern
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1482	whose number is 10 or more using this syntax because a sequence such as \50 is
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1483	interpreted as a character defined in octal. See the subsection entitled
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1484	"Non-printing characters"
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1485	<a href="#digitsafterbackslash">above</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1486	for further details of the handling of digits following a backslash. There is
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1487	no such problem when named parentheses are used. A back reference to any
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1488	subpattern is possible using named parentheses (see below).
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1489	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1490	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1491	Another way of avoiding the ambiguity inherent in the use of digits following a
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1492	backslash is to use the \g escape sequence, which is a feature introduced in
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1493	Perl 5.10. This escape must be followed by an unsigned number or a negative
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1494	number, optionally enclosed in braces. These examples are all identical:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1495	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1496	(ring), \1
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1497	(ring), \g1
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1498	(ring), \g{1}
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1499	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1500	An unsigned number specifies an absolute reference without the ambiguity that
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1501	is present in the older syntax. It is also useful when literal digits follow
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1502	the reference. A negative number is a relative reference. Consider this
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1503	example:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1504	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1505	(abc(def)ghi)\g{-1}
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1506	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1507	The sequence \g{-1} is a reference to the most recently started capturing
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1508	subpattern before \g, that is, is it equivalent to \2. Similarly, \g{-2}
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1509	would be equivalent to \1. The use of relative references can be helpful in
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1510	long patterns, and also in patterns that are created by joining together
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1511	fragments that contain references within themselves.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1512	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1513	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1514	A back reference matches whatever actually matched the capturing subpattern in
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1515	the current subject string, rather than anything matching the subpattern
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1516	itself (see
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1517	<a href="#subpatternsassubroutines">"Subpatterns as subroutines"</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1518	below for a way of doing that). So the pattern
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1519	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1520	(sens\|respons)e and \1ibility
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1521	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1522	matches "sense and sensibility" and "response and responsibility", but not
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1523	"sense and responsibility". If caseful matching is in force at the time of the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1524	back reference, the case of letters is relevant. For example,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1525	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1526	((?i)rah)\s+\1
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1527	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1528	matches "rah rah" and "RAH RAH", but not "RAH rah", even though the original
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1529	capturing subpattern is matched caselessly.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1530	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1531	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1532	There are several different ways of writing back references to named
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1533	subpatterns. The .NET syntax \k{name} and the Perl syntax \k<name> or
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1534	\k'name' are supported, as is the Python syntax (?P=name). Perl 5.10's unified
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1535	back reference syntax, in which \g can be used for both numeric and named
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1536	references, is also supported. We could rewrite the above example in any of
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1537	the following ways:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1538	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1539	(?<p1>(?i)rah)\s+\k<p1>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1540	(?'p1'(?i)rah)\s+\k{p1}
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1541	(?P<p1>(?i)rah)\s+(?P=p1)
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1542	(?<p1>(?i)rah)\s+\g{p1}
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1543	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1544	A subpattern that is referenced by name may appear in the pattern before or
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1545	after the reference.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1546	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1547	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1548	There may be more than one back reference to the same subpattern. If a
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1549	subpattern has not actually been used in a particular match, any back
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1550	references to it always fail. For example, the pattern
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1551	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1552	(a\|(bc))\2
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1553	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1554	always fails if it starts to match "a" rather than "bc". Because there may be
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1555	many capturing parentheses in a pattern, all digits following the backslash are
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1556	taken as part of a potential back reference number. If the pattern continues
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1557	with a digit character, some delimiter must be used to terminate the back
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1558	reference. If the PCRE_EXTENDED option is set, this can be whitespace.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1559	Otherwise an empty comment (see
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1560	<a href="#comments">"Comments"</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1561	below) can be used.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1562	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1563	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1564	A back reference that occurs inside the parentheses to which it refers fails
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1565	when the subpattern is first used, so, for example, (a\1) never matches.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1566	However, such references can be useful inside repeated subpatterns. For
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1567	example, the pattern
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1568	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1569	(a\|b\1)+
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1570	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1571	matches any number of "a"s and also "aba", "ababbaa" etc. At each iteration of
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1572	the subpattern, the back reference matches the character string corresponding
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1573	to the previous iteration. In order for this to work, the pattern must be such
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1574	that the first iteration does not need to match the back reference. This can be
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1575	done using alternation, as in the example above, or by a quantifier with a
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1576	minimum of zero.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1577	<a name="bigassertions"></a></P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1578	<br><a name="SEC18" href="#TOC1">ASSERTIONS</a><br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1579	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1580	An assertion is a test on the characters following or preceding the current
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1581	matching point that does not actually consume any characters. The simple
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1582	assertions coded as \b, \B, \A, \G, \Z, \z, ^ and $ are described
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1583	<a href="#smallassertions">above.</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1584	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1585	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1586	More complicated assertions are coded as subpatterns. There are two kinds:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1587	those that look ahead of the current position in the subject string, and those
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1588	that look behind it. An assertion subpattern is matched in the normal way,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1589	except that it does not cause the current matching position to be changed.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1590	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1591	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1592	Assertion subpatterns are not capturing subpatterns, and may not be repeated,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1593	because it makes no sense to assert the same thing several times. If any kind
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1594	of assertion contains capturing subpatterns within it, these are counted for
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1595	the purposes of numbering the capturing subpatterns in the whole pattern.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1596	However, substring capturing is carried out only for positive assertions,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1597	because it does not make sense for negative assertions.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1598	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1599	<br><b>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1600	Lookahead assertions
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1601	</b><br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1602	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1603	Lookahead assertions start with (?= for positive assertions and (?! for
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1604	negative assertions. For example,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1605	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1606	\w+(?=;)
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1607	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1608	matches a word followed by a semicolon, but does not include the semicolon in
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1609	the match, and
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1610	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1611	foo(?!bar)
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1612	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1613	matches any occurrence of "foo" that is not followed by "bar". Note that the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1614	apparently similar pattern
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1615	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1616	(?!foo)bar
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1617	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1618	does not find an occurrence of "bar" that is preceded by something other than
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1619	"foo"; it finds any occurrence of "bar" whatsoever, because the assertion
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1620	(?!foo) is always true when the next three characters are "bar". A
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1621	lookbehind assertion is needed to achieve the other effect.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1622	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1623	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1624	If you want to force a matching failure at some point in a pattern, the most
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1625	convenient way to do it is with (?!) because an empty string always matches, so
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1626	an assertion that requires there not to be an empty string must always fail.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1627	<a name="lookbehind"></a></P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1628	<br><b>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1629	Lookbehind assertions
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1630	</b><br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1631	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1632	Lookbehind assertions start with (?<= for positive assertions and (?<! for
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1633	negative assertions. For example,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1634	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1635	(?<!foo)bar
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1636	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1637	does find an occurrence of "bar" that is not preceded by "foo". The contents of
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1638	a lookbehind assertion are restricted such that all the strings it matches must
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1639	have a fixed length. However, if there are several top-level alternatives, they
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1640	do not all have to have the same fixed length. Thus
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1641	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1642	(?<=bullock\|donkey)
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1643	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1644	is permitted, but
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1645	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1646	(?<!dogs?\|cats?)
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1647	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1648	causes an error at compile time. Branches that match different length strings
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1649	are permitted only at the top level of a lookbehind assertion. This is an
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1650	extension compared with Perl (at least for 5.8), which requires all branches to
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1651	match the same length of string. An assertion such as
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1652	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1653	(?<=ab(c\|de))
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1654	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1655	is not permitted, because its single top-level branch can match two different
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1656	lengths, but it is acceptable if rewritten to use two top-level branches:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1657	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1658	(?<=abc\|abde)
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1659	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1660	In some cases, the Perl 5.10 escape sequence \K
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1661	<a href="#resetmatchstart">(see above)</a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1662	can be used instead of a lookbehind assertion; this is not restricted to a
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1663	fixed-length.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1664	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1665	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1666	The implementation of lookbehind assertions is, for each alternative, to
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1667	temporarily move the current position back by the fixed length and then try to
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1668	match. If there are insufficient characters before the current position, the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1669	assertion fails.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1670	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1671	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1672	PCRE does not allow the \C escape (which matches a single byte in UTF-8 mode)
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1673	to appear in lookbehind assertions, because it makes it impossible to calculate
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1674	the length of the lookbehind. The \X and \R escapes, which can match
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1675	different numbers of bytes, are also not permitted.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1676	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1677	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1678	Possessive quantifiers can be used in conjunction with lookbehind assertions to
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1679	specify efficient matching at the end of the subject string. Consider a simple
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1680	pattern such as
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1681	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1682	abcd$
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1683	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1684	when applied to a long string that does not match. Because matching proceeds
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1685	from left to right, PCRE will look for each "a" in the subject and then see if
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1686	what follows matches the rest of the pattern. If the pattern is specified as
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1687	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1688	^.*abcd$
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1689	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1690	the initial .* matches the entire string at first, but when this fails (because
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1691	there is no following "a"), it backtracks to match all but the last character,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1692	then all but the last two characters, and so on. Once again the search for "a"
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1693	covers the entire string, from right to left, so we are no better off. However,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1694	if the pattern is written as
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1695	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1696	^.*+(?<=abcd)
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1697	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1698	there can be no backtracking for the .*+ item; it can match only the entire
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1699	string. The subsequent lookbehind assertion does a single test on the last four
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1700	characters. If it fails, the match fails immediately. For long strings, this
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1701	approach makes a significant difference to the processing time.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1702	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1703	<br><b>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1704	Using multiple assertions
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1705	</b><br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1706	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1707	Several assertions (of any sort) may occur in succession. For example,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1708	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1709	(?<=\d{3})(?<!999)foo
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1710	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1711	matches "foo" preceded by three digits that are not "999". Notice that each of
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1712	the assertions is applied independently at the same point in the subject
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1713	string. First there is a check that the previous three characters are all
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1714	digits, and then there is a check that the same three characters are not "999".
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1715	This pattern does <i>not</i> match "foo" preceded by six characters, the first
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1716	of which are digits and the last three of which are not "999". For example, it
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1717	doesn't match "123abcfoo". A pattern to do that is
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1718	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1719	(?<=\d{3}...)(?<!999)foo
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1720	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1721	This time the first assertion looks at the preceding six characters, checking
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1722	that the first three are digits, and then the second assertion checks that the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1723	preceding three characters are not "999".
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1724	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1725	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1726	Assertions can be nested in any combination. For example,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1727	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1728	(?<=(?<!foo)bar)baz
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1729	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1730	matches an occurrence of "baz" that is preceded by "bar" which in turn is not
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1731	preceded by "foo", while
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1732	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1733	(?<=\d{3}(?!999)...)foo
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1734	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1735	is another pattern that matches "foo" preceded by three digits and any three
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1736	characters that are not "999".
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1737	<a name="conditions"></a></P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1738	<br><a name="SEC19" href="#TOC1">CONDITIONAL SUBPATTERNS</a><br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1739	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1740	It is possible to cause the matching process to obey a subpattern
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1741	conditionally or to choose between two alternative subpatterns, depending on
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1742	the result of an assertion, or whether a previous capturing subpattern matched
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1743	or not. The two possible forms of conditional subpattern are
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1744	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1745	(?(condition)yes-pattern)
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1746	(?(condition)yes-pattern\|no-pattern)
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1747	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1748	If the condition is satisfied, the yes-pattern is used; otherwise the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1749	no-pattern (if present) is used. If there are more than two alternatives in the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1750	subpattern, a compile-time error occurs.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1751	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1752	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1753	There are four kinds of condition: references to subpatterns, references to
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1754	recursion, a pseudo-condition called DEFINE, and assertions.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1755	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1756	<br><b>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1757	Checking for a used subpattern by number
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1758	</b><br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1759	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1760	If the text between the parentheses consists of a sequence of digits, the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1761	condition is true if the capturing subpattern of that number has previously
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1762	matched. An alternative notation is to precede the digits with a plus or minus
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1763	sign. In this case, the subpattern number is relative rather than absolute.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1764	The most recently opened parentheses can be referenced by (?(-1), the next most
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1765	recent by (?(-2), and so on. In looping constructs it can also make sense to
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1766	refer to subsequent groups with constructs such as (?(+2).
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1767	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1768	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1769	Consider the following pattern, which contains non-significant white space to
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1770	make it more readable (assume the PCRE_EXTENDED option) and to divide it into
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1771	three parts for ease of discussion:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1772	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1773	( $ )? [^()]+ (?(1) $ )
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1774	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1775	The first part matches an optional opening parenthesis, and if that
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1776	character is present, sets it as the first captured substring. The second part
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1777	matches one or more characters that are not parentheses. The third part is a
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1778	conditional subpattern that tests whether the first set of parentheses matched
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1779	or not. If they did, that is, if subject started with an opening parenthesis,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1780	the condition is true, and so the yes-pattern is executed and a closing
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1781	parenthesis is required. Otherwise, since no-pattern is not present, the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1782	subpattern matches nothing. In other words, this pattern matches a sequence of
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1783	non-parentheses, optionally enclosed in parentheses.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1784	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1785	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1786	If you were embedding this pattern in a larger one, you could use a relative
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1787	reference:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1788	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1789	...other stuff... ( $ )? [^()]+ (?(-1) $ ) ...
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1790	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1791	This makes the fragment independent of the parentheses in the larger pattern.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1792	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1793	<br><b>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1794	Checking for a used subpattern by name
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1795	</b><br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1796	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1797	Perl uses the syntax (?(<name>)...) or (?('name')...) to test for a used
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1798	subpattern by name. For compatibility with earlier versions of PCRE, which had
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1799	this facility before Perl, the syntax (?(name)...) is also recognized. However,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1800	there is a possible ambiguity with this syntax, because subpattern names may
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1801	consist entirely of digits. PCRE looks first for a named subpattern; if it
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1802	cannot find one and the name consists entirely of digits, PCRE looks for a
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1803	subpattern of that number, which must be greater than zero. Using subpattern
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1804	names that consist entirely of digits is not recommended.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1805	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1806	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1807	Rewriting the above example to use a named subpattern gives this:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1808	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1809	(?<OPEN> $ )? [^()]+ (?(<OPEN>) $ )
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1810
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1811	</PRE>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1812	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1813	<br><b>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1814	Checking for pattern recursion
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1815	</b><br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1816	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1817	If the condition is the string (R), and there is no subpattern with the name R,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1818	the condition is true if a recursive call to the whole pattern or any
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1819	subpattern has been made. If digits or a name preceded by ampersand follow the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1820	letter R, for example:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1821	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1822	(?(R3)...) or (?(R&name)...)
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1823	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1824	the condition is true if the most recent recursion is into the subpattern whose
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1825	number or name is given. This condition does not check the entire recursion
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1826	stack.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1827	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1828	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1829	At "top level", all these recursion test conditions are false. Recursive
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1830	patterns are described below.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1831	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1832	<br><b>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1833	Defining subpatterns for use by reference only
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1834	</b><br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1835	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1836	If the condition is the string (DEFINE), and there is no subpattern with the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1837	name DEFINE, the condition is always false. In this case, there may be only one
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1838	alternative in the subpattern. It is always skipped if control reaches this
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1839	point in the pattern; the idea of DEFINE is that it can be used to define
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1840	"subroutines" that can be referenced from elsewhere. (The use of "subroutines"
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1841	is described below.) For example, a pattern to match an IPv4 address could be
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1842	written like this (ignore whitespace and line breaks):
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1843	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1844	(?(DEFINE) (?<byte> 2[0-4]\d \| 25[0-5] \| 1\d\d \| [1-9]?\d) )
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1845	\b (?&byte) (\.(?&byte)){3} \b
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1846	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1847	The first part of the pattern is a DEFINE group inside which a another group
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1848	named "byte" is defined. This matches an individual component of an IPv4
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1849	address (a number less than 256). When matching takes place, this part of the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1850	pattern is skipped because DEFINE acts like a false condition.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1851	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1852	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1853	The rest of the pattern uses references to the named group to match the four
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1854	dot-separated components of an IPv4 address, insisting on a word boundary at
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1855	each end.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1856	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1857	<br><b>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1858	Assertion conditions
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1859	</b><br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1860	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1861	If the condition is not in any of the above formats, it must be an assertion.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1862	This may be a positive or negative lookahead or lookbehind assertion. Consider
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1863	this pattern, again containing non-significant white space, and with the two
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1864	alternatives on the second line:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1865	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1866	(?(?=[^a-z]*[a-z])
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1867	\d{2}-[a-z]{3}-\d{2} \| \d{2}-\d{2}-\d{2} )
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1868	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1869	The condition is a positive lookahead assertion that matches an optional
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1870	sequence of non-letters followed by a letter. In other words, it tests for the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1871	presence of at least one letter in the subject. If a letter is found, the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1872	subject is matched against the first alternative; otherwise it is matched
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1873	against the second. This pattern matches strings in one of the two forms
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1874	dd-aaa-dd or dd-dd-dd, where aaa are letters and dd are digits.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1875	<a name="comments"></a></P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1876	<br><a name="SEC20" href="#TOC1">COMMENTS</a><br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1877	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1878	The sequence (?# marks the start of a comment that continues up to the next
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1879	closing parenthesis. Nested parentheses are not permitted. The characters
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1880	that make up a comment play no part in the pattern matching at all.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1881	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1882	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1883	If the PCRE_EXTENDED option is set, an unescaped # character outside a
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1884	character class introduces a comment that continues to immediately after the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1885	next newline in the pattern.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1886	<a name="recursion"></a></P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1887	<br><a name="SEC21" href="#TOC1">RECURSIVE PATTERNS</a><br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1888	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1889	Consider the problem of matching a string in parentheses, allowing for
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1890	unlimited nested parentheses. Without the use of recursion, the best that can
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1891	be done is to use a pattern that matches up to some fixed depth of nesting. It
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1892	is not possible to handle an arbitrary nesting depth.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1893	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1894	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1895	For some time, Perl has provided a facility that allows regular expressions to
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1896	recurse (amongst other things). It does this by interpolating Perl code in the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1897	expression at run time, and the code can refer to the expression itself. A Perl
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1898	pattern using code interpolation to solve the parentheses problem can be
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1899	created like this:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1900	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1901	$re = qr{$ (?: (?>[^()]+) \| (?p{$re}) )* $}x;
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1902	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1903	The (?p{...}) item interpolates Perl code at run time, and in this case refers
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1904	recursively to the pattern in which it appears.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1905	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1906	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1907	Obviously, PCRE cannot support the interpolation of Perl code. Instead, it
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1908	supports special syntax for recursion of the entire pattern, and also for
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1909	individual subpattern recursion. After its introduction in PCRE and Python,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1910	this kind of recursion was introduced into Perl at release 5.10.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1911	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1912	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1913	A special item that consists of (? followed by a number greater than zero and a
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1914	closing parenthesis is a recursive call of the subpattern of the given number,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1915	provided that it occurs inside that subpattern. (If not, it is a "subroutine"
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1916	call, which is described in the next section.) The special item (?R) or (?0) is
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1917	a recursive call of the entire regular expression.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1918	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1919	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1920	In PCRE (like Python, but unlike Perl), a recursive subpattern call is always
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1921	treated as an atomic group. That is, once it has matched some of the subject
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1922	string, it is never re-entered, even if it contains untried alternatives and
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1923	there is a subsequent matching failure.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1924	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1925	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1926	This PCRE pattern solves the nested parentheses problem (assume the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1927	PCRE_EXTENDED option is set so that white space is ignored):
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1928	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1929	$ ( (?>[^()]+) \| (?R) )* $
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1930	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1931	First it matches an opening parenthesis. Then it matches any number of
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1932	substrings which can either be a sequence of non-parentheses, or a recursive
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1933	match of the pattern itself (that is, a correctly parenthesized substring).
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1934	Finally there is a closing parenthesis.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1935	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1936	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1937	If this were part of a larger pattern, you would not want to recurse the entire
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1938	pattern, so instead you could use this:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1939	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1940	( $ ( (?>[^()]+) \| (?1) )* $ )
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1941	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1942	We have put the pattern into parentheses, and caused the recursion to refer to
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1943	them instead of the whole pattern.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1944	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1945	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1946	In a larger pattern, keeping track of parenthesis numbers can be tricky. This
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1947	is made easier by the use of relative references. (A Perl 5.10 feature.)
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1948	Instead of (?1) in the pattern above you can write (?-2) to refer to the second
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1949	most recently opened parentheses preceding the recursion. In other words, a
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1950	negative number counts capturing parentheses leftwards from the point at which
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1951	it is encountered.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1952	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1953	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1954	It is also possible to refer to subsequently opened parentheses, by writing
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1955	references such as (?+2). However, these cannot be recursive because the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1956	reference is not inside the parentheses that are referenced. They are always
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1957	"subroutine" calls, as described in the next section.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1958	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1959	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1960	An alternative approach is to use named parentheses instead. The Perl syntax
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1961	for this is (?&name); PCRE's earlier syntax (?P>name) is also supported. We
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1962	could rewrite the above example as follows:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1963	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1964	(?<pn> $ ( (?>[^()]+) \| (?&pn) )* $ )
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1965	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1966	If there is more than one subpattern with the same name, the earliest one is
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1967	used.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1968	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1969	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1970	This particular example pattern that we have been looking at contains nested
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1971	unlimited repeats, and so the use of atomic grouping for matching strings of
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1972	non-parentheses is important when applying the pattern to strings that do not
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1973	match. For example, when this pattern is applied to
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1974	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1975	(aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa()
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1976	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1977	it yields "no match" quickly. However, if atomic grouping is not used,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1978	the match runs for a very long time indeed because there are so many different
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1979	ways the + and * repeats can carve up the subject, and all have to be tested
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1980	before failure can be reported.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1981	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1982	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1983	At the end of a match, the values set for any capturing subpatterns are those
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1984	from the outermost level of the recursion at which the subpattern value is set.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1985	If you want to obtain intermediate values, a callout function can be used (see
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1986	below and the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1987	<a href="pcrecallout.html"><b>pcrecallout</b></a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1988	documentation). If the pattern above is matched against
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1989	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1990	(ab(cd)ef)
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1991	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1992	the value for the capturing parentheses is "ef", which is the last value taken
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1993	on at the top level. If additional parentheses are added, giving
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1994	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1995	$ ( ( (?>[^()]+) \| (?R) )* ) $
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1996	^ ^
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1997	^ ^
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1998	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	1999	the string they capture is "ab(cd)ef", the contents of the top level
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2000	parentheses. If there are more than 15 capturing parentheses in a pattern, PCRE
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2001	has to obtain extra memory to store data during a recursion, which it does by
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2002	using <b>pcre_malloc</b>, freeing it via <b>pcre_free</b> afterwards. If no
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2003	memory can be obtained, the match fails with the PCRE_ERROR_NOMEMORY error.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2004	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2005	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2006	Do not confuse the (?R) item with the condition (R), which tests for recursion.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2007	Consider this pattern, which matches text in angle brackets, allowing for
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2008	arbitrary nesting. Only digits are allowed in nested brackets (that is, when
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2009	recursing), whereas any characters are permitted at the outer level.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2010	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2011	< (?: (?(R) \d++ \| [^<>]+) \| (?R)) >
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2012	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2013	In this pattern, (?(R) is the start of a conditional subpattern, with two
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2014	different alternatives for the recursive and non-recursive cases. The (?R) item
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2015	is the actual recursive call.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2016	<a name="subpatternsassubroutines"></a></P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2017	<br><a name="SEC22" href="#TOC1">SUBPATTERNS AS SUBROUTINES</a><br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2018	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2019	If the syntax for a recursive subpattern reference (either by number or by
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2020	name) is used outside the parentheses to which it refers, it operates like a
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2021	subroutine in a programming language. The "called" subpattern may be defined
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2022	before or after the reference. A numbered reference can be absolute or
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2023	relative, as in these examples:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2024	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2025	(...(absolute)...)...(?2)...
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2026	(...(relative)...)...(?-1)...
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2027	(...(?+1)...(relative)...
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2028	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2029	An earlier example pointed out that the pattern
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2030	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2031	(sens\|respons)e and \1ibility
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2032	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2033	matches "sense and sensibility" and "response and responsibility", but not
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2034	"sense and responsibility". If instead the pattern
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2035	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2036	(sens\|respons)e and (?1)ibility
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2037	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2038	is used, it does match "sense and responsibility" as well as the other two
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2039	strings. Another example is given in the discussion of DEFINE above.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2040	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2041	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2042	Like recursive subpatterns, a "subroutine" call is always treated as an atomic
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2043	group. That is, once it has matched some of the subject string, it is never
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2044	re-entered, even if it contains untried alternatives and there is a subsequent
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2045	matching failure.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2046	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2047	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2048	When a subpattern is used as a subroutine, processing options such as
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2049	case-independence are fixed when the subpattern is defined. They cannot be
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2050	changed for different calls. For example, consider this pattern:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2051	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2052	(abc)(?i:(?-1))
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2053	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2054	It matches "abcabc". It does not match "abcABC" because the change of
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2055	processing option does not affect the called subpattern.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2056	<a name="onigurumasubroutines"></a></P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2057	<br><a name="SEC23" href="#TOC1">ONIGURUMA SUBROUTINE SYNTAX</a><br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2058	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2059	For compatibility with Oniguruma, the non-Perl syntax \g followed by a name or
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2060	a number enclosed either in angle brackets or single quotes, is an alternative
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2061	syntax for referencing a subpattern as a subroutine, possibly recursively. Here
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2062	are two of the examples used above, rewritten using this syntax:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2063	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2064	(?<pn> $ ( (?>[^()]+) \| \g<pn> )* $ )
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2065	(sens\|respons)e and \g'1'ibility
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2066	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2067	PCRE supports an extension to Oniguruma: if a number is preceded by a
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2068	plus or a minus sign it is taken as a relative reference. For example:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2069	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2070	(abc)(?i:\g<-1>)
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2071	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2072	Note that \g{...} (Perl syntax) and \g<...> (Oniguruma syntax) are <i>not</i>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2073	synonymous. The former is a back reference; the latter is a subroutine call.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2074	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2075	<br><a name="SEC24" href="#TOC1">CALLOUTS</a><br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2076	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2077	Perl has a feature whereby using the sequence (?{...}) causes arbitrary Perl
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2078	code to be obeyed in the middle of matching a regular expression. This makes it
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2079	possible, amongst other things, to extract different substrings that match the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2080	same pair of parentheses when there is a repetition.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2081	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2082	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2083	PCRE provides a similar feature, but of course it cannot obey arbitrary Perl
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2084	code. The feature is called "callout". The caller of PCRE provides an external
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2085	function by putting its entry point in the global variable <i>pcre_callout</i>.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2086	By default, this variable contains NULL, which disables all calling out.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2087	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2088	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2089	Within a regular expression, (?C) indicates the points at which the external
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2090	function is to be called. If you want to identify different callout points, you
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2091	can put a number less than 256 after the letter C. The default value is zero.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2092	For example, this pattern has two callout points:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2093	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2094	(?C1)abc(?C2)def
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2095	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2096	If the PCRE_AUTO_CALLOUT flag is passed to <b>pcre_compile()</b>, callouts are
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2097	automatically installed before each item in the pattern. They are all numbered
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2098	255.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2099	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2100	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2101	During matching, when PCRE reaches a callout point (and <i>pcre_callout</i> is
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2102	set), the external function is called. It is provided with the number of the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2103	callout, the position in the pattern, and, optionally, one item of data
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2104	originally supplied by the caller of <b>pcre_exec()</b>. The callout function
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2105	may cause matching to proceed, to backtrack, or to fail altogether. A complete
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2106	description of the interface to the callout function is given in the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2107	<a href="pcrecallout.html"><b>pcrecallout</b></a>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2108	documentation.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2109	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2110	<br><a name="SEC25" href="#TOC1">BACKTRACKING CONTROL</a><br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2111	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2112	Perl 5.10 introduced a number of "Special Backtracking Control Verbs", which
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2113	are described in the Perl documentation as "experimental and subject to change
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2114	or removal in a future version of Perl". It goes on to say: "Their usage in
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2115	production code should be noted to avoid problems during upgrades." The same
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2116	remarks apply to the PCRE features described in this section.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2117	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2118	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2119	Since these verbs are specifically related to backtracking, most of them can be
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2120	used only when the pattern is to be matched using <b>pcre_exec()</b>, which uses
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2121	a backtracking algorithm. With the exception of (*FAIL), which behaves like a
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2122	failing negative assertion, they cause an error if encountered by
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2123	<b>pcre_dfa_exec()</b>.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2124	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2125	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2126	The new verbs make use of what was previously invalid syntax: an opening
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2127	parenthesis followed by an asterisk. In Perl, they are generally of the form
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2128	(*VERB:ARG) but PCRE does not support the use of arguments, so its general
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2129	form is just (*VERB). Any number of these verbs may occur in a pattern. There
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2130	are two kinds:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2131	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2132	<br><b>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2133	Verbs that act immediately
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2134	</b><br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2135	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2136	The following verbs act as soon as they are encountered:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2137	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2138	(*ACCEPT)
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2139	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2140	This verb causes the match to end successfully, skipping the remainder of the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2141	pattern. When inside a recursion, only the innermost pattern is ended
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2142	immediately. PCRE differs from Perl in what happens if the (*ACCEPT) is inside
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2143	capturing parentheses. In Perl, the data so far is captured: in PCRE no data is
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2144	captured. For example:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2145	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2146	A(A\|B(*ACCEPT)\|C)D
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2147	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2148	This matches "AB", "AAD", or "ACD", but when it matches "AB", no data is
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2149	captured.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2150	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2151	(FAIL) or (F)
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2152	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2153	This verb causes the match to fail, forcing backtracking to occur. It is
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2154	equivalent to (?!) but easier to read. The Perl documentation notes that it is
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2155	probably useful only when combined with (?{}) or (??{}). Those are, of course,
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2156	Perl features that are not present in PCRE. The nearest equivalent is the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2157	callout feature, as for example in this pattern:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2158	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2159	a+(?C)(*FAIL)
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2160	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2161	A match with the string "aaaa" always fails, but the callout is taken before
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2162	each backtrack happens (in this example, 10 times).
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2163	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2164	<br><b>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2165	Verbs that act after backtracking
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2166	</b><br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2167	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2168	The following verbs do nothing when they are encountered. Matching continues
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2169	with what follows, but if there is no subsequent match, a failure is forced.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2170	The verbs differ in exactly what kind of failure occurs.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2171	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2172	(*COMMIT)
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2173	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2174	This verb causes the whole match to fail outright if the rest of the pattern
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2175	does not match. Even if the pattern is unanchored, no further attempts to find
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2176	a match by advancing the start point take place. Once (*COMMIT) has been
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2177	passed, <b>pcre_exec()</b> is committed to finding a match at the current
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2178	starting point, or not at all. For example:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2179	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2180	a+(*COMMIT)b
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2181	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2182	This matches "xxaab" but not "aacaab". It can be thought of as a kind of
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2183	dynamic anchor, or "I've started, so I must finish."
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2184	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2185	(*PRUNE)
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2186	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2187	This verb causes the match to fail at the current position if the rest of the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2188	pattern does not match. If the pattern is unanchored, the normal "bumpalong"
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2189	advance to the next starting character then happens. Backtracking can occur as
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2190	usual to the left of (PRUNE), or when matching to the right of (PRUNE), but
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2191	if there is no match to the right, backtracking cannot cross (*PRUNE).
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2192	In simple cases, the use of (*PRUNE) is just an alternative to an atomic
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2193	group or possessive quantifier, but there are some uses of (*PRUNE) that cannot
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2194	be expressed in any other way.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2195	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2196	(*SKIP)
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2197	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2198	This verb is like (*PRUNE), except that if the pattern is unanchored, the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2199	"bumpalong" advance is not to the next character, but to the position in the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2200	subject where (SKIP) was encountered. (SKIP) signifies that whatever text
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2201	was matched leading up to it cannot be part of a successful match. Consider:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2202	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2203	a+(*SKIP)b
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2204	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2205	If the subject is "aaaac...", after the first match attempt fails (starting at
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2206	the first character in the string), the starting point skips on to start the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2207	next attempt at "c". Note that a possessive quantifer does not have the same
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2208	effect in this example; although it would suppress backtracking during the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2209	first match attempt, the second attempt would start at the second character
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2210	instead of skipping on to "c".
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2211	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2212	(*THEN)
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2213	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2214	This verb causes a skip to the next alternation if the rest of the pattern does
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2215	not match. That is, it cancels pending backtracking, but only within the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2216	current alternation. Its name comes from the observation that it can be used
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2217	for a pattern-based if-then-else block:
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2218	<pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2219	( COND1 (THEN) FOO \| COND2 (THEN) BAR \| COND3 (*THEN) BAZ ) ...
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2220	</pre>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2221	If the COND1 pattern matches, FOO is tried (and possibly further items after
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2222	the end of the group if FOO succeeds); on failure the matcher skips to the
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2223	second alternative and tries COND2, without backtracking into COND1. If (*THEN)
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2224	is used outside of any alternation, it acts exactly like (*PRUNE).
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2225	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2226	<br><a name="SEC26" href="#TOC1">SEE ALSO</a><br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2227	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2228	<b>pcreapi</b>(3), <b>pcrecallout</b>(3), <b>pcrematching</b>(3), <b>pcre</b>(3).
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2229	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2230	<br><a name="SEC27" href="#TOC1">AUTHOR</a><br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2231	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2232	Philip Hazel
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2233	<br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2234	University Computing Service
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2235	<br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2236	Cambridge CB2 3QH, England.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2237	<br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2238	</P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2239	<br><a name="SEC28" href="#TOC1">REVISION</a><br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2240	<P>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2241	Last updated: 19 April 2008
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2242	<br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2243	Copyright © 1997-2008 University of Cambridge.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2244	<br>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2245	<p>
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2246	Return to the <a href="index.html">PCRE index page</a>.
7f656887cf89 First submission to Symbian Foundation staging server. Tom Sutcliffe <thomas.sutcliffe@accenture.com> parents: diff changeset	2247	</p>

author	Tom Sutcliffe <thomas.sutcliffe@accenture.com>
	Sat, 31 Jul 2010 19:07:57 +0100
changeset 23	092bcc217d9d
parent 0	7f656887cf89
permissions	-rw-r--r--