1 .TH PCREPOSIX 3

     2 .SH NAME

     3 PCRE - Perl-compatible regular expressions.

     4 .SH "SYNOPSIS OF POSIX API"

     5 .rs

     6 .sp

     7 .B #include <pcreposix.h>

     8 .PP

     9 .SM

    10 .B int regcomp(regex_t *\fIpreg\fP, const char *\fIpattern\fP,

    11 .ti +5n

    12 .B int \fIcflags\fP);

    13 .PP

    14 .B int regexec(regex_t *\fIpreg\fP, const char *\fIstring\fP,

    15 .ti +5n

    16 .B size_t \fInmatch\fP, regmatch_t \fIpmatch\fP[], int \fIeflags\fP);

    17 .PP

    18 .B size_t regerror(int \fIerrcode\fP, const regex_t *\fIpreg\fP,

    19 .ti +5n

    20 .B char *\fIerrbuf\fP, size_t \fIerrbuf_size\fP);

    21 .PP

    22 .B void regfree(regex_t *\fIpreg\fP);

    23 .

    24 .SH DESCRIPTION

    25 .rs

    26 .sp

    27 This set of functions provides a POSIX-style API to the PCRE regular expression

    28 package. See the

    29 .\" HREF

    30 \fBpcreapi\fP

    31 .\"

    32 documentation for a description of PCRE's native API, which contains much

    33 additional functionality.

    34 .P

    35 The functions described here are just wrapper functions that ultimately call

    36 the PCRE native API. Their prototypes are defined in the \fBpcreposix.h\fP

    37 header file, and on Unix systems the library itself is called

    38 \fBpcreposix.a\fP, so can be accessed by adding \fB-lpcreposix\fP to the

    39 command for linking an application that uses them. Because the POSIX functions

    40 call the native ones, it is also necessary to add \fB-lpcre\fP.

    41 .P

    42 I have implemented only those option bits that can be reasonably mapped to PCRE

    43 native options. In addition, the option REG_EXTENDED is defined with the value

    44 zero. This has no effect, but since programs that are written to the POSIX

    45 interface often use it, this makes it easier to slot in PCRE as a replacement

    46 library. Other POSIX options are not even defined.

    47 .P

    48 When PCRE is called via these functions, it is only the API that is POSIX-like

    49 in style. The syntax and semantics of the regular expressions themselves are

    50 still those of Perl, subject to the setting of various PCRE options, as

    51 described below. "POSIX-like in style" means that the API approximates to the

    52 POSIX definition; it is not fully POSIX-compatible, and in multi-byte encoding

    53 domains it is probably even less compatible.

    54 .P

    55 The header for these functions is supplied as \fBpcreposix.h\fP to avoid any

    56 potential clash with other POSIX libraries. It can, of course, be renamed or

    57 aliased as \fBregex.h\fP, which is the "correct" name. It provides two

    58 structure types, \fIregex_t\fP for compiled internal forms, and

    59 \fIregmatch_t\fP for returning captured substrings. It also defines some

    60 constants whose names start with "REG_"; these are used for setting options and

    61 identifying error codes.

    62 .P

    63 .SH "COMPILING A PATTERN"

    64 .rs

    65 .sp

    66 The function \fBregcomp()\fP is called to compile a pattern into an

    67 internal form. The pattern is a C string terminated by a binary zero, and

    68 is passed in the argument \fIpattern\fP. The \fIpreg\fP argument is a pointer

    69 to a \fBregex_t\fP structure that is used as a base for storing information

    70 about the compiled regular expression.

    71 .P

    72 The argument \fIcflags\fP is either zero, or contains one or more of the bits

    73 defined by the following macros:

    74 .sp

    75   REG_DOTALL

    76 .sp

    77 The PCRE_DOTALL option is set when the regular expression is passed for

    78 compilation to the native function. Note that REG_DOTALL is not part of the

    79 POSIX standard.

    80 .sp

    81   REG_ICASE

    82 .sp

    83 The PCRE_CASELESS option is set when the regular expression is passed for

    84 compilation to the native function.

    85 .sp

    86   REG_NEWLINE

    87 .sp

    88 The PCRE_MULTILINE option is set when the regular expression is passed for

    89 compilation to the native function. Note that this does \fInot\fP mimic the

    90 defined POSIX behaviour for REG_NEWLINE (see the following section).

    91 .sp

    92   REG_NOSUB

    93 .sp

    94 The PCRE_NO_AUTO_CAPTURE option is set when the regular expression is passed

    95 for compilation to the native function. In addition, when a pattern that is

    96 compiled with this flag is passed to \fBregexec()\fP for matching, the

    97 \fInmatch\fP and \fIpmatch\fP arguments are ignored, and no captured strings

    98 are returned.

    99 .sp

   100   REG_UTF8

   101 .sp

   102 The PCRE_UTF8 option is set when the regular expression is passed for

   103 compilation to the native function. This causes the pattern itself and all data

   104 strings used for matching it to be treated as UTF-8 strings. Note that REG_UTF8

   105 is not part of the POSIX standard.

   106 .P

   107 In the absence of these flags, no options are passed to the native function.

   108 This means the the regex is compiled with PCRE default semantics. In

   109 particular, the way it handles newline characters in the subject string is the

   110 Perl way, not the POSIX way. Note that setting PCRE_MULTILINE has only

   111 \fIsome\fP of the effects specified for REG_NEWLINE. It does not affect the way

   112 newlines are matched by . (they aren't) or by a negative class such as [^a]

   113 (they are).

   114 .P

   115 The yield of \fBregcomp()\fP is zero on success, and non-zero otherwise. The

   116 \fIpreg\fP structure is filled in on success, and one member of the structure

   117 is public: \fIre_nsub\fP contains the number of capturing subpatterns in

   118 the regular expression. Various error codes are defined in the header file.

   119 .

   120 .

   121 .SH "MATCHING NEWLINE CHARACTERS"

   122 .rs

   123 .sp

   124 This area is not simple, because POSIX and Perl take different views of things.

   125 It is not possible to get PCRE to obey POSIX semantics, but then PCRE was never

   126 intended to be a POSIX engine. The following table lists the different

   127 possibilities for matching newline characters in PCRE:

   128 .sp

   129                           Default   Change with

   130 .sp

   131   . matches newline          no     PCRE_DOTALL

   132   newline matches [^a]       yes    not changeable

   133   $ matches \en at end        yes    PCRE_DOLLARENDONLY

   134   $ matches \en in middle     no     PCRE_MULTILINE

   135   ^ matches \en in middle     no     PCRE_MULTILINE

   136 .sp

   137 This is the equivalent table for POSIX:

   138 .sp

   139                           Default   Change with

   140 .sp

   141   . matches newline          yes    REG_NEWLINE

   142   newline matches [^a]       yes    REG_NEWLINE

   143   $ matches \en at end        no     REG_NEWLINE

   144   $ matches \en in middle     no     REG_NEWLINE

   145   ^ matches \en in middle     no     REG_NEWLINE

   146 .sp

   147 PCRE's behaviour is the same as Perl's, except that there is no equivalent for

   148 PCRE_DOLLAR_ENDONLY in Perl. In both PCRE and Perl, there is no way to stop

   149 newline from matching [^a].

   150 .P

   151 The default POSIX newline handling can be obtained by setting PCRE_DOTALL and

   152 PCRE_DOLLAR_ENDONLY, but there is no way to make PCRE behave exactly as for the

   153 REG_NEWLINE action.

   154 .

   155 .

   156 .SH "MATCHING A PATTERN"

   157 .rs

   158 .sp

   159 The function \fBregexec()\fP is called to match a compiled pattern \fIpreg\fP

   160 against a given \fIstring\fP, which is by default terminated by a zero byte

   161 (but see REG_STARTEND below), subject to the options in \fIeflags\fP. These can

   162 be:

   163 .sp

   164   REG_NOTBOL

   165 .sp

   166 The PCRE_NOTBOL option is set when calling the underlying PCRE matching

   167 function.

   168 .sp

   169   REG_NOTEOL

   170 .sp

   171 The PCRE_NOTEOL option is set when calling the underlying PCRE matching

   172 function.

   173 .sp

   174   REG_STARTEND

   175 .sp

   176 The string is considered to start at \fIstring\fP + \fIpmatch[0].rm_so\fP and

   177 to have a terminating NUL located at \fIstring\fP + \fIpmatch[0].rm_eo\fP

   178 (there need not actually be a NUL at that location), regardless of the value of

   179 \fInmatch\fP. This is a BSD extension, compatible with but not specified by

   180 IEEE Standard 1003.2 (POSIX.2), and should be used with caution in software

   181 intended to be portable to other systems. Note that a non-zero \fIrm_so\fP does

   182 not imply REG_NOTBOL; REG_STARTEND affects only the location of the string, not

   183 how it is matched.

   184 .P

   185 If the pattern was compiled with the REG_NOSUB flag, no data about any matched

   186 strings is returned. The \fInmatch\fP and \fIpmatch\fP arguments of

   187 \fBregexec()\fP are ignored.

   188 .P

   189 Otherwise,the portion of the string that was matched, and also any captured

   190 substrings, are returned via the \fIpmatch\fP argument, which points to an

   191 array of \fInmatch\fP structures of type \fIregmatch_t\fP, containing the

   192 members \fIrm_so\fP and \fIrm_eo\fP. These contain the offset to the first

   193 character of each substring and the offset to the first character after the end

   194 of each substring, respectively. The 0th element of the vector relates to the

   195 entire portion of \fIstring\fP that was matched; subsequent elements relate to

   196 the capturing subpatterns of the regular expression. Unused entries in the

   197 array have both structure members set to -1.

   198 .P

   199 A successful match yields a zero return; various error codes are defined in the

   200 header file, of which REG_NOMATCH is the "expected" failure code.

   201 .

   202 .

   203 .SH "ERROR MESSAGES"

   204 .rs

   205 .sp

   206 The \fBregerror()\fP function maps a non-zero errorcode from either

   207 \fBregcomp()\fP or \fBregexec()\fP to a printable message. If \fIpreg\fP is not

   208 NULL, the error should have arisen from the use of that structure. A message

   209 terminated by a binary zero is placed in \fIerrbuf\fP. The length of the

   210 message, including the zero, is limited to \fIerrbuf_size\fP. The yield of the

   211 function is the size of buffer needed to hold the whole message.

   212 .

   213 .

   214 .SH MEMORY USAGE

   215 .rs

   216 .sp

   217 Compiling a regular expression causes memory to be allocated and associated

   218 with the \fIpreg\fP structure. The function \fBregfree()\fP frees all such

   219 memory, after which \fIpreg\fP may no longer be used as a compiled expression.

   220 .

   221 .

   222 .SH AUTHOR

   223 .rs

   224 .sp

   225 .nf

   226 Philip Hazel

   227 University Computing Service

   228 Cambridge CB2 3QH, England.

   229 .fi

   230 .

   231 .

   232 .SH REVISION

   233 .rs

   234 .sp

   235 .nf

   236 Last updated: 05 April 2008

   237 Copyright (c) 1997-2008 University of Cambridge.

   238 .fi