.TH PCREBUILD 3

.SH NAME

PCRE - Perl-compatible regular expressions

.SH "PCRE BUILD-TIME OPTIONS"

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This document describes the optional features of PCRE that can be selected when

the library is compiled. It assumes use of the \fBconfigure\fP script, where

the optional features are selected or deselected by providing options to

\fBconfigure\fP before running the \fBmake\fP command. However, the same

options can be selected in both Unix-like and non-Unix-like environments using

the GUI facility of \fBCMakeSetup\fP if you are using \fBCMake\fP instead of

\fBconfigure\fP to build PCRE.

.P

The complete list of options for \fBconfigure\fP (which includes the standard

ones such as the selection of the installation directory) can be obtained by

running

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  ./configure --help

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The following sections include descriptions of options whose names begin with

--enable or --disable. These settings specify changes to the defaults for the

\fBconfigure\fP command. Because of the way that \fBconfigure\fP works,

--enable and --disable always come in pairs, so the complementary option always

exists as well, but as it specifies the default, it is not described.

.

.SH "C++ SUPPORT"

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By default, the \fBconfigure\fP script will search for a C++ compiler and C++

header files. If it finds them, it automatically builds the C++ wrapper library

for PCRE. You can disable this by adding

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  --disable-cpp

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to the \fBconfigure\fP command.

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.SH "UTF-8 SUPPORT"

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To build PCRE with support for UTF-8 character strings, add

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  --enable-utf8

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to the \fBconfigure\fP command. Of itself, this does not make PCRE treat

strings as UTF-8. As well as compiling PCRE with this option, you also have

have to set the PCRE_UTF8 option when you call the \fBpcre_compile()\fP

function.

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.SH "UNICODE CHARACTER PROPERTY SUPPORT"

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UTF-8 support allows PCRE to process character values greater than 255 in the

strings that it handles. On its own, however, it does not provide any

facilities for accessing the properties of such characters. If you want to be

able to use the pattern escapes \eP, \ep, and \eX, which refer to Unicode

character properties, you must add

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  --enable-unicode-properties

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to the \fBconfigure\fP command. This implies UTF-8 support, even if you have

not explicitly requested it.

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Including Unicode property support adds around 30K of tables to the PCRE

library. Only the general category properties such as \fILu\fP and \fINd\fP are

supported. Details are given in the

.\" HREF

\fBpcrepattern\fP

.\"

documentation.

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.SH "CODE VALUE OF NEWLINE"

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By default, PCRE interprets character 10 (linefeed, LF) as indicating the end

of a line. This is the normal newline character on Unix-like systems. You can

compile PCRE to use character 13 (carriage return, CR) instead, by adding

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  --enable-newline-is-cr

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to the \fBconfigure\fP command. There is also a --enable-newline-is-lf option,

which explicitly specifies linefeed as the newline character.

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Alternatively, you can specify that line endings are to be indicated by the two

character sequence CRLF. If you want this, add

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  --enable-newline-is-crlf

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to the \fBconfigure\fP command. There is a fourth option, specified by

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  --enable-newline-is-anycrlf

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which causes PCRE to recognize any of the three sequences CR, LF, or CRLF as

indicating a line ending. Finally, a fifth option, specified by

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  --enable-newline-is-any

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causes PCRE to recognize any Unicode newline sequence.

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Whatever line ending convention is selected when PCRE is built can be

overridden when the library functions are called. At build time it is

conventional to use the standard for your operating system.

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.SH "WHAT \eR MATCHES"

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By default, the sequence \eR in a pattern matches any Unicode newline sequence,

whatever has been selected as the line ending sequence. If you specify

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  --enable-bsr-anycrlf

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the default is changed so that \eR matches only CR, LF, or CRLF. Whatever is

selected when PCRE is built can be overridden when the library functions are

called.

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.SH "BUILDING SHARED AND STATIC LIBRARIES"

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The PCRE building process uses \fBlibtool\fP to build both shared and static

Unix libraries by default. You can suppress one of these by adding one of

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  --disable-shared

  --disable-static

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to the \fBconfigure\fP command, as required.

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.SH "POSIX MALLOC USAGE"

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When PCRE is called through the POSIX interface (see the

.\" HREF

\fBpcreposix\fP

.\"

documentation), additional working storage is required for holding the pointers

to capturing substrings, because PCRE requires three integers per substring,

whereas the POSIX interface provides only two. If the number of expected

substrings is small, the wrapper function uses space on the stack, because this

is faster than using \fBmalloc()\fP for each call. The default threshold above

which the stack is no longer used is 10; it can be changed by adding a setting

such as

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  --with-posix-malloc-threshold=20

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to the \fBconfigure\fP command.

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.SH "HANDLING VERY LARGE PATTERNS"

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Within a compiled pattern, offset values are used to point from one part to

another (for example, from an opening parenthesis to an alternation

metacharacter). By default, two-byte values are used for these offsets, leading

to a maximum size for a compiled pattern of around 64K. This is sufficient to

handle all but the most gigantic patterns. Nevertheless, some people do want to

process enormous patterns, so it is possible to compile PCRE to use three-byte

or four-byte offsets by adding a setting such as

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  --with-link-size=3

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to the \fBconfigure\fP command. The value given must be 2, 3, or 4. Using

longer offsets slows down the operation of PCRE because it has to load

additional bytes when handling them.

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.SH "AVOIDING EXCESSIVE STACK USAGE"

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When matching with the \fBpcre_exec()\fP function, PCRE implements backtracking

by making recursive calls to an internal function called \fBmatch()\fP. In

environments where the size of the stack is limited, this can severely limit

PCRE's operation. (The Unix environment does not usually suffer from this

problem, but it may sometimes be necessary to increase the maximum stack size.

There is a discussion in the

.\" HREF

\fBpcrestack\fP

.\"

documentation.) An alternative approach to recursion that uses memory from the

heap to remember data, instead of using recursive function calls, has been

implemented to work round the problem of limited stack size. If you want to

build a version of PCRE that works this way, add

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  --disable-stack-for-recursion

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to the \fBconfigure\fP command. With this configuration, PCRE will use the

\fBpcre_stack_malloc\fP and \fBpcre_stack_free\fP variables to call memory

management functions. By default these point to \fBmalloc()\fP and

\fBfree()\fP, but you can replace the pointers so that your own functions are

used.

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Separate functions are provided rather than using \fBpcre_malloc\fP and

\fBpcre_free\fP because the usage is very predictable: the block sizes

requested are always the same, and the blocks are always freed in reverse

order. A calling program might be able to implement optimized functions that

perform better than \fBmalloc()\fP and \fBfree()\fP. PCRE runs noticeably more

slowly when built in this way. This option affects only the \fBpcre_exec()\fP

function; it is not relevant for the the \fBpcre_dfa_exec()\fP function.

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.SH "LIMITING PCRE RESOURCE USAGE"

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Internally, PCRE has a function called \fBmatch()\fP, which it calls repeatedly

(sometimes recursively) when matching a pattern with the \fBpcre_exec()\fP

function. By controlling the maximum number of times this function may be

called during a single matching operation, a limit can be placed on the

resources used by a single call to \fBpcre_exec()\fP. The limit can be changed

at run time, as described in the

.\" HREF

\fBpcreapi\fP

.\"

documentation. The default is 10 million, but this can be changed by adding a

setting such as

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  --with-match-limit=500000

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to the \fBconfigure\fP command. This setting has no effect on the

\fBpcre_dfa_exec()\fP matching function.

.P

In some environments it is desirable to limit the depth of recursive calls of

\fBmatch()\fP more strictly than the total number of calls, in order to

restrict the maximum amount of stack (or heap, if --disable-stack-for-recursion

is specified) that is used. A second limit controls this; it defaults to the

value that is set for --with-match-limit, which imposes no additional

constraints. However, you can set a lower limit by adding, for example,

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  --with-match-limit-recursion=10000

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to the \fBconfigure\fP command. This value can also be overridden at run time.

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.SH "CREATING CHARACTER TABLES AT BUILD TIME"

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PCRE uses fixed tables for processing characters whose code values are less

than 256. By default, PCRE is built with a set of tables that are distributed

in the file \fIpcre_chartables.c.dist\fP. These tables are for ASCII codes

only. If you add

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  --enable-rebuild-chartables

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to the \fBconfigure\fP command, the distributed tables are no longer used.

Instead, a program called \fBdftables\fP is compiled and run. This outputs the

source for new set of tables, created in the default locale of your C runtime

system. (This method of replacing the tables does not work if you are cross

compiling, because \fBdftables\fP is run on the local host. If you need to

create alternative tables when cross compiling, you will have to do so "by

hand".)

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.SH "USING EBCDIC CODE"

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PCRE assumes by default that it will run in an environment where the character

code is ASCII (or Unicode, which is a superset of ASCII). This is the case for

most computer operating systems. PCRE can, however, be compiled to run in an

EBCDIC environment by adding

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  --enable-ebcdic

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to the \fBconfigure\fP command. This setting implies

--enable-rebuild-chartables. You should only use it if you know that you are in

an EBCDIC environment (for example, an IBM mainframe operating system).

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.SH "PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT"

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By default, \fBpcregrep\fP reads all files as plain text. You can build it so

that it recognizes files whose names end in \fB.gz\fP or \fB.bz2\fP, and reads

them with \fBlibz\fP or \fBlibbz2\fP, respectively, by adding one or both of

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  --enable-pcregrep-libz

  --enable-pcregrep-libbz2

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to the \fBconfigure\fP command. These options naturally require that the

relevant libraries are installed on your system. Configuration will fail if

they are not.

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.SH "PCRETEST OPTION FOR LIBREADLINE SUPPORT"

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If you add

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  --enable-pcretest-libreadline

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to the \fBconfigure\fP command, \fBpcretest\fP is linked with the

\fBlibreadline\fP library, and when its input is from a terminal, it reads it

using the \fBreadline()\fP function. This provides line-editing and history

facilities. Note that \fBlibreadline\fP is GPL-licenced, so if you distribute a

binary of \fBpcretest\fP linked in this way, there may be licensing issues.

.P

Setting this option causes the \fB-lreadline\fP option to be added to the

\fBpcretest\fP build. In many operating environments with a sytem-installed

\fBlibreadline\fP this is sufficient. However, in some environments (e.g.

if an unmodified distribution version of readline is in use), some extra

configuration may be necessary. The INSTALL file for \fBlibreadline\fP says

this:

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  "Readline uses the termcap functions, but does not link with the

  termcap or curses library itself, allowing applications which link

  with readline the to choose an appropriate library."

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If your environment has not been set up so that an appropriate library is

automatically included, you may need to add something like

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  LIBS="-ncurses"

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immediately before the \fBconfigure\fP command.

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.SH "SEE ALSO"

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\fBpcreapi\fP(3), \fBpcre_config\fP(3).

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.SH AUTHOR

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Philip Hazel

University Computing Service

Cambridge CB2 3QH, England.

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.

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.SH REVISION

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Last updated: 13 April 2008

Copyright (c) 1997-2008 University of Cambridge.

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