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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<HTML><HEAD><TITLE>Man page of PCRE2POSIX</TITLE>
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</HEAD><BODY>
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<H1>PCRE2POSIX</H1>
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Section: C Library Functions (3)<BR>Updated: 30 January 2019<BR><A HREF="#index">Index</A>
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<A HREF="/cgi-bin/man/man2html">Return to Main Contents</A><HR>
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<A NAME="lbAB"> </A>
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<H2>NAME</H2>
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PCRE2 - Perl-compatible regular expressions (revised API)
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<A NAME="lbAC"> </A>
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<H2>SYNOPSIS</H2>
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<P>
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<B>#include <<A HREF="file:///usr/include/pcre2posix.h">pcre2posix.h</A>></B>
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<P>
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<PRE>
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<B>int pcre2_regcomp(regex_t *</B><I>preg</I>, const char *<I>pattern</I>,
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<B> int </B><I>cflags</I>);
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<B>int pcre2_regexec(const regex_t *</B><I>preg</I>, const char *<I>string</I>,
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<B> size_t </B><I>nmatch</I>, regmatch_t <I>pmatch</I>[], int <I>eflags</I>);
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<B>size_t pcre2_regerror(int </B><I>errcode</I>, const regex_t *<I>preg</I>,
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<B> char *</B><I>errbuf</I>, size_t <I>errbuf_size</I>);
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<B>void pcre2_regfree(regex_t *</B><I>preg</I>);
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</PRE>
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<A NAME="lbAD"> </A>
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<H2>DESCRIPTION</H2>
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<P>
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This set of functions provides a POSIX-style API for the PCRE2 regular
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expression 8-bit library. There are no POSIX-style wrappers for PCRE2's 16-bit
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and 32-bit libraries. See the
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<B>pcre2api</B>
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documentation for a description of PCRE2's native API, which contains much
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additional functionality.
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<P>
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The functions described here are wrapper functions that ultimately call the
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PCRE2 native API. Their prototypes are defined in the <B>pcre2posix.h</B> header
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file, and they all have unique names starting with <B>pcre2_</B>. However, the
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<B>pcre2posix.h</B> header also contains macro definitions that convert the
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standard POSIX names such <B>regcomp()</B> into <B>pcre2_regcomp()</B> etc. This
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means that a program can use the usual POSIX names without running the risk of
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accidentally linking with POSIX functions from a different library.
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<P>
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On Unix-like systems the PCRE2 POSIX library is called <B>libpcre2-posix</B>, so
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can be accessed by adding <B>-lpcre2-posix</B> to the command for linking an
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application. Because the POSIX functions call the native ones, it is also
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necessary to add <B>-lpcre2-8</B>.
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<P>
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Although they are not defined as protypes in <B>pcre2posix.h</B>, the library
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does contain functions with the POSIX names <B>regcomp()</B> etc. These simply
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pass their arguments to the PCRE2 functions. These functions are provided for
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backwards compatibility with earlier versions of PCRE2, so that existing
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programs do not have to be recompiled.
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<P>
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Calling the header file <B>pcre2posix.h</B> avoids any conflict with other POSIX
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libraries. It can, of course, be renamed or aliased as <B>regex.h</B>, which is
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the "correct" name, if there is no clash. It provides two structure types,
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<I>regex_t</I> for compiled internal forms, and <I>regmatch_t</I> for returning
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captured substrings. It also defines some constants whose names start with
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"REG_"; these are used for setting options and identifying error codes.
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<A NAME="lbAE"> </A>
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<H2>USING THE POSIX FUNCTIONS</H2>
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<P>
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Those POSIX option bits that can reasonably be mapped to PCRE2 native options
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have been implemented. In addition, the option REG_EXTENDED is defined with the
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value zero. This has no effect, but since programs that are written to the
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POSIX interface often use it, this makes it easier to slot in PCRE2 as a
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replacement library. Other POSIX options are not even defined.
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<P>
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There are also some options that are not defined by POSIX. These have been
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added at the request of users who want to make use of certain PCRE2-specific
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features via the POSIX calling interface or to add BSD or GNU functionality.
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<P>
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When PCRE2 is called via these functions, it is only the API that is POSIX-like
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in style. The syntax and semantics of the regular expressions themselves are
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still those of Perl, subject to the setting of various PCRE2 options, as
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described below. "POSIX-like in style" means that the API approximates to the
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POSIX definition; it is not fully POSIX-compatible, and in multi-unit encoding
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domains it is probably even less compatible.
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<P>
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The descriptions below use the actual names of the functions, but, as described
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above, the standard POSIX names (without the <B>pcre2_</B> prefix) may also be
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used.
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<A NAME="lbAF"> </A>
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<H2>COMPILING A PATTERN</H2>
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<P>
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The function <B>pcre2_regcomp()</B> is called to compile a pattern into an
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internal form. By default, the pattern is a C string terminated by a binary
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zero (but see REG_PEND below). The <I>preg</I> argument is a pointer to a
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<B>regex_t</B> structure that is used as a base for storing information about
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the compiled regular expression. (It is also used for input when REG_PEND is
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set.)
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<P>
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The argument <I>cflags</I> is either zero, or contains one or more of the bits
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defined by the following macros:
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<P>
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<BR> REG_DOTALL
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<P>
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The PCRE2_DOTALL option is set when the regular expression is passed for
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compilation to the native function. Note that REG_DOTALL is not part of the
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POSIX standard.
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<P>
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<BR> REG_ICASE
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<P>
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The PCRE2_CASELESS option is set when the regular expression is passed for
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compilation to the native function.
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<P>
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<BR> REG_NEWLINE
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<P>
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The PCRE2_MULTILINE option is set when the regular expression is passed for
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compilation to the native function. Note that this does <I>not</I> mimic the
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defined POSIX behaviour for REG_NEWLINE (see the following section).
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<P>
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<BR> REG_NOSPEC
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<P>
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The PCRE2_LITERAL option is set when the regular expression is passed for
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compilation to the native function. This disables all meta characters in the
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pattern, causing it to be treated as a literal string. The only other options
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that are allowed with REG_NOSPEC are REG_ICASE, REG_NOSUB, REG_PEND, and
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REG_UTF. Note that REG_NOSPEC is not part of the POSIX standard.
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<P>
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<BR> REG_NOSUB
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<P>
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When a pattern that is compiled with this flag is passed to
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<B>pcre2_regexec()</B> for matching, the <I>nmatch</I> and <I>pmatch</I> arguments
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are ignored, and no captured strings are returned. Versions of the PCRE library
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prior to 10.22 used to set the PCRE2_NO_AUTO_CAPTURE compile option, but this
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no longer happens because it disables the use of backreferences.
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<P>
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<BR> REG_PEND
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<P>
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If this option is set, the <B>reg_endp</B> field in the <I>preg</I> structure
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(which has the type const char *) must be set to point to the character beyond
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the end of the pattern before calling <B>pcre2_regcomp()</B>. The pattern itself
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may now contain binary zeros, which are treated as data characters. Without
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REG_PEND, a binary zero terminates the pattern and the <B>re_endp</B> field is
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ignored. This is a GNU extension to the POSIX standard and should be used with
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caution in software intended to be portable to other systems.
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<P>
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<BR> REG_UCP
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<P>
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The PCRE2_UCP option is set when the regular expression is passed for
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compilation to the native function. This causes PCRE2 to use Unicode properties
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when matchine \d, \w, etc., instead of just recognizing ASCII values. Note
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that REG_UCP is not part of the POSIX standard.
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<P>
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<BR> REG_UNGREEDY
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<P>
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The PCRE2_UNGREEDY option is set when the regular expression is passed for
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compilation to the native function. Note that REG_UNGREEDY is not part of the
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POSIX standard.
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<P>
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<BR> REG_UTF
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<P>
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The PCRE2_UTF option is set when the regular expression is passed for
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compilation to the native function. This causes the pattern itself and all data
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strings used for matching it to be treated as UTF-8 strings. Note that REG_UTF
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is not part of the POSIX standard.
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<P>
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In the absence of these flags, no options are passed to the native function.
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This means the the regex is compiled with PCRE2 default semantics. In
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particular, the way it handles newline characters in the subject string is the
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Perl way, not the POSIX way. Note that setting PCRE2_MULTILINE has only
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<I>some</I> of the effects specified for REG_NEWLINE. It does not affect the way
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newlines are matched by the dot metacharacter (they are not) or by a negative
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class such as [^a] (they are).
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<P>
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The yield of <B>pcre2_regcomp()</B> is zero on success, and non-zero otherwise.
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The <I>preg</I> structure is filled in on success, and one other member of the
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structure (as well as <I>re_endp</I>) is public: <I>re_nsub</I> contains the
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number of capturing subpatterns in the regular expression. Various error codes
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are defined in the header file.
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<P>
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NOTE: If the yield of <B>pcre2_regcomp()</B> is non-zero, you must not attempt
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to use the contents of the <I>preg</I> structure. If, for example, you pass it
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to <B>pcre2_regexec()</B>, the result is undefined and your program is likely to
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crash.
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<A NAME="lbAG"> </A>
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<H2>MATCHING NEWLINE CHARACTERS</H2>
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<P>
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This area is not simple, because POSIX and Perl take different views of things.
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It is not possible to get PCRE2 to obey POSIX semantics, but then PCRE2 was
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never intended to be a POSIX engine. The following table lists the different
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possibilities for matching newline characters in Perl and PCRE2:
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<P>
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<BR> Default Change with
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<P>
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<BR> . matches newline no PCRE2_DOTALL
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<BR> newline matches [^a] yes not changeable
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<BR> $ matches \n at end yes PCRE2_DOLLAR_ENDONLY
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<BR> $ matches \n in middle no PCRE2_MULTILINE
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<BR> ^ matches \n in middle no PCRE2_MULTILINE
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<P>
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This is the equivalent table for a POSIX-compatible pattern matcher:
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<P>
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<BR> Default Change with
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<P>
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<BR> . matches newline yes REG_NEWLINE
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<BR> newline matches [^a] yes REG_NEWLINE
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<BR> $ matches \n at end no REG_NEWLINE
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<BR> $ matches \n in middle no REG_NEWLINE
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<BR> ^ matches \n in middle no REG_NEWLINE
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<P>
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This behaviour is not what happens when PCRE2 is called via its POSIX
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API. By default, PCRE2's behaviour is the same as Perl's, except that there is
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no equivalent for PCRE2_DOLLAR_ENDONLY in Perl. In both PCRE2 and Perl, there
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is no way to stop newline from matching [^a].
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<P>
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Default POSIX newline handling can be obtained by setting PCRE2_DOTALL and
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PCRE2_DOLLAR_ENDONLY when calling <B>pcre2_compile()</B> directly, but there is
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no way to make PCRE2 behave exactly as for the REG_NEWLINE action. When using
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the POSIX API, passing REG_NEWLINE to PCRE2's <B>pcre2_regcomp()</B> function
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causes PCRE2_MULTILINE to be passed to <B>pcre2_compile()</B>, and REG_DOTALL
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passes PCRE2_DOTALL. There is no way to pass PCRE2_DOLLAR_ENDONLY.
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<A NAME="lbAH"> </A>
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<H2>MATCHING A PATTERN</H2>
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<P>
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The function <B>pcre2_regexec()</B> is called to match a compiled pattern
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<I>preg</I> against a given <I>string</I>, which is by default terminated by a
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zero byte (but see REG_STARTEND below), subject to the options in <I>eflags</I>.
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These can be:
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<P>
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<BR> REG_NOTBOL
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<P>
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The PCRE2_NOTBOL option is set when calling the underlying PCRE2 matching
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function.
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<P>
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<BR> REG_NOTEMPTY
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<P>
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The PCRE2_NOTEMPTY option is set when calling the underlying PCRE2 matching
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function. Note that REG_NOTEMPTY is not part of the POSIX standard. However,
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setting this option can give more POSIX-like behaviour in some situations.
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<P>
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<BR> REG_NOTEOL
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<P>
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The PCRE2_NOTEOL option is set when calling the underlying PCRE2 matching
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function.
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<P>
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<BR> REG_STARTEND
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<P>
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When this option is set, the subject string starts at <I>string</I> +
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<I>pmatch[0].rm_so</I> and ends at <I>string</I> + <I>pmatch[0].rm_eo</I>, which
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should point to the first character beyond the string. There may be binary
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zeros within the subject string, and indeed, using REG_STARTEND is the only
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way to pass a subject string that contains a binary zero.
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<P>
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Whatever the value of <I>pmatch[0].rm_so</I>, the offsets of the matched string
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and any captured substrings are still given relative to the start of
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<I>string</I> itself. (Before PCRE2 release 10.30 these were given relative to
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<I>string</I> + <I>pmatch[0].rm_so</I>, but this differs from other
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implementations.)
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<P>
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This is a BSD extension, compatible with but not specified by IEEE Standard
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1003.2 (POSIX.2), and should be used with caution in software intended to be
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portable to other systems. Note that a non-zero <I>rm_so</I> does not imply
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REG_NOTBOL; REG_STARTEND affects only the location and length of the string,
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not how it is matched. Setting REG_STARTEND and passing <I>pmatch</I> as NULL
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are mutually exclusive; the error REG_INVARG is returned.
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<P>
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If the pattern was compiled with the REG_NOSUB flag, no data about any matched
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strings is returned. The <I>nmatch</I> and <I>pmatch</I> arguments of
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<B>pcre2_regexec()</B> are ignored (except possibly as input for REG_STARTEND).
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<P>
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The value of <I>nmatch</I> may be zero, and the value <I>pmatch</I> may be NULL
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(unless REG_STARTEND is set); in both these cases no data about any matched
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strings is returned.
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<P>
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Otherwise, the portion of the string that was matched, and also any captured
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substrings, are returned via the <I>pmatch</I> argument, which points to an
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array of <I>nmatch</I> structures of type <I>regmatch_t</I>, containing the
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members <I>rm_so</I> and <I>rm_eo</I>. These contain the byte offset to the first
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character of each substring and the offset to the first character after the end
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of each substring, respectively. The 0th element of the vector relates to the
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entire portion of <I>string</I> that was matched; subsequent elements relate to
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the capturing subpatterns of the regular expression. Unused entries in the
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array have both structure members set to -1.
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<P>
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A successful match yields a zero return; various error codes are defined in the
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header file, of which REG_NOMATCH is the "expected" failure code.
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<A NAME="lbAI"> </A>
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<H2>ERROR MESSAGES</H2>
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<P>
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The <B>pcre2_regerror()</B> function maps a non-zero errorcode from either
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<B>pcre2_regcomp()</B> or <B>pcre2_regexec()</B> to a printable message. If
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<I>preg</I> is not NULL, the error should have arisen from the use of that
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structure. A message terminated by a binary zero is placed in <I>errbuf</I>. If
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the buffer is too short, only the first <I>errbuf_size</I> - 1 characters of the
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error message are used. The yield of the function is the size of buffer needed
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to hold the whole message, including the terminating zero. This value is
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greater than <I>errbuf_size</I> if the message was truncated.
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<A NAME="lbAJ"> </A>
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<H2>MEMORY USAGE</H2>
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<P>
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Compiling a regular expression causes memory to be allocated and associated
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with the <I>preg</I> structure. The function <B>pcre2_regfree()</B> frees all
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such memory, after which <I>preg</I> may no longer be used as a compiled
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expression.
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<A NAME="lbAK"> </A>
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<H2>AUTHOR</H2>
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<P>
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<PRE>
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Philip Hazel
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University Computing Service
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Cambridge, England.
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</PRE>
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<A NAME="lbAL"> </A>
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<H2>REVISION</H2>
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<P>
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<PRE>
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Last updated: 30 January 2019
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Copyright (c) 1997-2019 University of Cambridge.
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</PRE>
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<P>
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<HR>
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<A NAME="index"> </A><H2>Index</H2>
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<DL>
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<DT id="1"><A HREF="#lbAB">NAME</A><DD>
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<DT id="2"><A HREF="#lbAC">SYNOPSIS</A><DD>
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<DT id="3"><A HREF="#lbAD">DESCRIPTION</A><DD>
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<DT id="4"><A HREF="#lbAE">USING THE POSIX FUNCTIONS</A><DD>
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<DT id="5"><A HREF="#lbAF">COMPILING A PATTERN</A><DD>
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<DT id="6"><A HREF="#lbAG">MATCHING NEWLINE CHARACTERS</A><DD>
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<DT id="7"><A HREF="#lbAH">MATCHING A PATTERN</A><DD>
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<DT id="8"><A HREF="#lbAI">ERROR MESSAGES</A><DD>
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<DT id="9"><A HREF="#lbAJ">MEMORY USAGE</A><DD>
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<DT id="10"><A HREF="#lbAK">AUTHOR</A><DD>
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<DT id="11"><A HREF="#lbAL">REVISION</A><DD>
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</DL>
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<HR>
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This document was created by
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<A HREF="/cgi-bin/man/man2html">man2html</A>,
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using the manual pages.<BR>
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Time: 00:05:50 GMT, March 31, 2021
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</BODY>
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