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<TITLE>pcreposix specification</TITLE>
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<body bgcolor="#FFFFFF" text="#00005A">
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<H1>pcreposix specification</H1>
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This HTML document has been generated automatically from the original man page.
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If there is any nonsense in it, please consult the man page in case the
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<LI><A NAME="TOC1" HREF="#SEC1">NAME</A>
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<LI><A NAME="TOC2" HREF="#SEC2">SYNOPSIS</A>
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<LI><A NAME="TOC3" HREF="#SEC3">DESCRIPTION</A>
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<LI><A NAME="TOC4" HREF="#SEC4">COMPILING A PATTERN</A>
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<LI><A NAME="TOC5" HREF="#SEC5">MATCHING A PATTERN</A>
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<LI><A NAME="TOC6" HREF="#SEC6">ERROR MESSAGES</A>
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<LI><A NAME="TOC7" HREF="#SEC7">STORAGE</A>
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<LI><A NAME="TOC8" HREF="#SEC8">AUTHOR</A>
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<LI><A NAME="SEC1" HREF="#TOC1">NAME</A>
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pcreposix - POSIX API for Perl-compatible regular expressions.
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<LI><A NAME="SEC2" HREF="#TOC1">SYNOPSIS</A>
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<B>#include <pcreposix.h></B>
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<B>int regcomp(regex_t *<I>preg</I>, const char *<I>pattern</I>,</B>
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<B>int <I>cflags</I>);</B>
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<B>int regexec(regex_t *<I>preg</I>, const char *<I>string</I>,</B>
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<B>size_t <I>nmatch</I>, regmatch_t <I>pmatch</I>[], int <I>eflags</I>);</B>
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<B>size_t regerror(int <I>errcode</I>, const regex_t *<I>preg</I>,</B>
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<B>char *<I>errbuf</I>, size_t <I>errbuf_size</I>);</B>
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<B>void regfree(regex_t *<I>preg</I>);</B>
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<LI><A NAME="SEC3" HREF="#TOC1">DESCRIPTION</A>
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This set of functions provides a POSIX-style API to the PCRE regular expression
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package. See the <B>pcre</B> documentation for a description of the native API,
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which contains additional functionality.
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The functions described here are just wrapper functions that ultimately call
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the native API. Their prototypes are defined in the <B>pcreposix.h</B> header
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file, and on Unix systems the library itself is called <B>pcreposix.a</B>, so
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can be accessed by adding <B>-lpcreposix</B> to the command for linking an
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application which uses them. Because the POSIX functions call the native ones,
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it is also necessary to add \fR-lpcre\fR.
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I have implemented only those option bits that can be reasonably mapped to PCRE
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native options. In addition, the options REG_EXTENDED and REG_NOSUB are defined
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with the value zero. They have no effect, but since programs that are written
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to the POSIX interface often use them, this makes it easier to slot in PCRE as
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a replacement library. Other POSIX options are not even defined.
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When PCRE 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 PCRE options, as
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The header for these functions is supplied as <B>pcreposix.h</B> to avoid any
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potential clash with other POSIX libraries. It can, of course, be renamed or
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aliased as <B>regex.h</B>, which is the "correct" name. It provides two
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structure types, <I>regex_t</I> for compiled internal forms, and
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<I>regmatch_t</I> for returning captured substrings. It also defines some
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constants whose names start with "REG_"; these are used for setting options and
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identifying error codes.
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<LI><A NAME="SEC4" HREF="#TOC1">COMPILING A PATTERN</A>
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The function <B>regcomp()</B> is called to compile a pattern into an
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internal form. The pattern is a C string terminated by a binary zero, and
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is passed in the argument <I>pattern</I>. The <I>preg</I> argument is a pointer
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to a regex_t structure which is used as a base for storing information about
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the compiled expression.
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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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The PCRE_CASELESS option is set when the expression is passed for compilation
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to the native function.
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The PCRE_MULTILINE option is set when the expression is passed for compilation
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to the native function.
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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 PCRE 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 PCRE_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 . (they aren't) or a negative class such as [^a] (they
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The yield of <B>regcomp()</B> is zero on success, and non-zero otherwise. The
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<I>preg</I> structure is filled in on success, and one member of the structure
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is publicized: <I>re_nsub</I> contains the number of capturing subpatterns in
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the regular expression. Various error codes are defined in the header file.
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<LI><A NAME="SEC5" HREF="#TOC1">MATCHING A PATTERN</A>
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The function <B>regexec()</B> is called to match a pre-compiled pattern
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<I>preg</I> against a given <I>string</I>, which is terminated by a zero byte,
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subject to the options in <I>eflags</I>. These can be:
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The PCRE_NOTBOL option is set when calling the underlying PCRE matching
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The PCRE_NOTEOL option is set when calling the underlying PCRE matching
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The portion of the string that was matched, and also any captured substrings,
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are returned via the <I>pmatch</I> argument, which points to an array of
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<I>nmatch</I> structures of type <I>regmatch_t</I>, containing the members
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<I>rm_so</I> and <I>rm_eo</I>. These contain the offset to the first character of
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each substring and the offset to the first character after the end of each
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substring, respectively. The 0th element of the vector relates to the entire
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portion of <I>string</I> that was matched; subsequent elements relate to the
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capturing subpatterns of the regular expression. Unused entries in the array
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have both structure members set to -1.
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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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<LI><A NAME="SEC6" HREF="#TOC1">ERROR MESSAGES</A>
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The <B>regerror()</B> function maps a non-zero errorcode from either
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<B>regcomp</B> or <B>regexec</B> to a printable message. If <I>preg</I> is not
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NULL, the error should have arisen from the use of that structure. A message
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terminated by a binary zero is placed in <I>errbuf</I>. The length of the
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message, including the zero, is limited to <I>errbuf_size</I>. The yield of the
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function is the size of buffer needed to hold the whole message.
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<LI><A NAME="SEC7" HREF="#TOC1">STORAGE</A>
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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>regfree()</B> frees all such
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memory, after which <I>preg</I> may no longer be used as a compiled expression.
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<LI><A NAME="SEC8" HREF="#TOC1">AUTHOR</A>
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Philip Hazel <ph10@cam.ac.uk>
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University Computing Service,
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Cambridge CB2 3QG, England.
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Phone: +44 1223 334714
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Copyright (c) 1997-2000 University of Cambridge.
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