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<html><head><title>pcre2posix specification</title></head><body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB"><h1>pcre2posix man page</h1><p>Return to the <a href="index.html">PCRE2 index page</a>.</p><p>This page is part of the PCRE2 HTML documentation. It was generatedautomatically from the original man page. If there is any nonsense in it,please consult the man page, in case the conversion went wrong.<br><ul><li><a name="TOC1" href="#SEC1">SYNOPSIS</a><li><a name="TOC2" href="#SEC2">DESCRIPTION</a><li><a name="TOC3" href="#SEC3">USING THE POSIX FUNCTIONS</a><li><a name="TOC4" href="#SEC4">COMPILING A PATTERN</a><li><a name="TOC5" href="#SEC5">MATCHING NEWLINE CHARACTERS</a><li><a name="TOC6" href="#SEC6">MATCHING A PATTERN</a><li><a name="TOC7" href="#SEC7">ERROR MESSAGES</a><li><a name="TOC8" href="#SEC8">MEMORY USAGE</a><li><a name="TOC9" href="#SEC9">AUTHOR</a><li><a name="TOC10" href="#SEC10">REVISION</a></ul><br><a name="SEC1" href="#TOC1">SYNOPSIS</a><br><P><b>#include <pcre2posix.h></b></P><P><b>int pcre2_regcomp(regex_t *<i>preg</i>, const char *<i>pattern</i>,</b><b> int <i>cflags</i>);</b><br><br><b>int pcre2_regexec(const regex_t *<i>preg</i>, const char *<i>string</i>,</b><b> size_t <i>nmatch</i>, regmatch_t <i>pmatch</i>[], int <i>eflags</i>);</b><br><br><b>size_t pcre2_regerror(int <i>errcode</i>, const regex_t *<i>preg</i>,</b><b> char *<i>errbuf</i>, size_t <i>errbuf_size</i>);</b><br><br><b>void pcre2_regfree(regex_t *<i>preg</i>);</b></P><br><a name="SEC2" href="#TOC1">DESCRIPTION</a><br><P>This set of functions provides a POSIX-style API for the PCRE2 regularexpression 8-bit library. There are no POSIX-style wrappers for PCRE2's 16-bitand 32-bit libraries. See the<a href="pcre2api.html"><b>pcre2api</b></a>documentation for a description of PCRE2's native API, which contains muchadditional functionality.</P><P><b>IMPORTANT NOTE</b>: The functions described here are NOT thread-safe, andshould not be used in multi-threaded applications. They are also limited toprocessing subjects that are not bigger than 2GB. Use the native API instead.</P><P>These functions are wrapper functions that ultimately call the PCRE2 nativeAPI. Their prototypes are defined in the <b>pcre2posix.h</b> header file, andthey all have unique names starting with <b>pcre2_</b>. However, the<b>pcre2posix.h</b> header also contains macro definitions that convert thestandard POSIX names such <b>regcomp()</b> into <b>pcre2_regcomp()</b> etc. Thismeans that a program can use the usual POSIX names without running the risk ofaccidentally linking with POSIX functions from a different library.</P><P>On Unix-like systems the PCRE2 POSIX library is called <b>libpcre2-posix</b>, socan be accessed by adding <b>-lpcre2-posix</b> to the command for linking anapplication. Because the POSIX functions call the native ones, it is alsonecessary to add <b>-lpcre2-8</b>.</P><P>On Windows systems, if you are linking to a DLL version of the library, it isrecommended that <b>PCRE2POSIX_SHARED</b> is defined before including the<b>pcre2posix.h</b> header, as it will allow for a more efficient way toinvoke the functions by adding the <b>__declspec(dllimport)</b> decorator.</P><P>Although they were not defined as prototypes in <b>pcre2posix.h</b>, releases10.33 to 10.36 of the library contained functions with the POSIX names<b>regcomp()</b> etc. These simply passed their arguments to the PCRE2functions. These functions were provided for backwards compatibility withearlier versions of PCRE2, which had only POSIX names. However, this has provedtroublesome in situations where a program links with several libraries, some ofwhich use PCRE2's POSIX interface while others use the real POSIX functions.For this reason, the POSIX names have been removed since release 10.37.</P><P>Calling the header file <b>pcre2posix.h</b> avoids any conflict with other POSIXlibraries. It can, of course, be renamed or aliased as <b>regex.h</b>, which isthe "correct" name, if there is no clash. It provides two structure types,<i>regex_t</i> for compiled internal forms, and <i>regmatch_t</i> for returningcaptured substrings. It also defines some constants whose names start with"REG_"; these are used for setting options and identifying error codes.</P><br><a name="SEC3" href="#TOC1">USING THE POSIX FUNCTIONS</a><br><P>Note that these functions are just POSIX-style wrappers for PCRE2's native API.They do not give POSIX regular expression behaviour, and they are notthread-safe or even POSIX compatible.</P><P>Those POSIX option bits that can reasonably be mapped to PCRE2 native optionshave been implemented. In addition, the option REG_EXTENDED is defined with thevalue zero. This has no effect, but since programs that are written to thePOSIX interface often use it, this makes it easier to slot in PCRE2 as areplacement library. Other POSIX options are not even defined.</P><P>There are also some options that are not defined by POSIX. These have beenadded at the request of users who want to make use of certain PCRE2-specificfeatures via the POSIX calling interface or to add BSD or GNU functionality.</P><P>When PCRE2 is called via these functions, it is only the API that is POSIX-likein style. The syntax and semantics of the regular expressions themselves arestill those of Perl, subject to the setting of various PCRE2 options, asdescribed below. "POSIX-like in style" means that the API approximates to thePOSIX definition; it is not fully POSIX-compatible, and in multi-unit encodingdomains it is probably even less compatible.</P><P>The descriptions below use the actual names of the functions, but, as describedabove, the standard POSIX names (without the <b>pcre2_</b> prefix) may also beused.</P><br><a name="SEC4" href="#TOC1">COMPILING A PATTERN</a><br><P>The function <b>pcre2_regcomp()</b> is called to compile a pattern into aninternal form. By default, the pattern is a C string terminated by a binaryzero (but see REG_PEND below). The <i>preg</i> argument is a pointer to a<b>regex_t</b> structure that is used as a base for storing information aboutthe compiled regular expression. It is also used for input when REG_PEND isset. The <b>regex_t</b> structure used by <b>pcre2_regcomp()</b> is defined in<b>pcre2posix.h</b> and is not the same as the structure used by other librariesthat provide POSIX-style matching.</P><P>The argument <i>cflags</i> is either zero, or contains one or more of the bitsdefined by the following macros:<pre> REG_DOTALL</pre>The PCRE2_DOTALL option is set when the regular expression is passed forcompilation to the native function. Note that REG_DOTALL is not part of thePOSIX standard.<pre> REG_ICASE</pre>The PCRE2_CASELESS option is set when the regular expression is passed forcompilation to the native function.<pre> REG_NEWLINE</pre>The PCRE2_MULTILINE option is set when the regular expression is passed forcompilation to the native function. Note that this does <i>not</i> mimic thedefined POSIX behaviour for REG_NEWLINE (see the following section).<pre> REG_NOSPEC</pre>The PCRE2_LITERAL option is set when the regular expression is passed forcompilation to the native function. This disables all meta characters in thepattern, causing it to be treated as a literal string. The only other optionsthat are allowed with REG_NOSPEC are REG_ICASE, REG_NOSUB, REG_PEND, andREG_UTF. Note that REG_NOSPEC is not part of the POSIX standard.<pre> REG_NOSUB</pre>When a pattern that is compiled with this flag is passed to<b>pcre2_regexec()</b> for matching, the <i>nmatch</i> and <i>pmatch</i> argumentsare ignored, and no captured strings are returned. Versions of the PCRE libraryprior to 10.22 used to set the PCRE2_NO_AUTO_CAPTURE compile option, but thisno longer happens because it disables the use of backreferences.<pre> REG_PEND</pre>If this option is set, the <b>reg_endp</b> field in the <i>preg</i> structure(which has the type const char *) must be set to point to the character beyondthe end of the pattern before calling <b>pcre2_regcomp()</b>. The pattern itselfmay now contain binary zeros, which are treated as data characters. WithoutREG_PEND, a binary zero terminates the pattern and the <b>re_endp</b> field isignored. This is a GNU extension to the POSIX standard and should be used withcaution in software intended to be portable to other systems.<pre> REG_UCP</pre>The PCRE2_UCP option is set when the regular expression is passed forcompilation to the native function. This causes PCRE2 to use Unicode propertieswhen matching \d, \w, etc., instead of just recognizing ASCII values. Notethat REG_UCP is not part of the POSIX standard.<pre> REG_UNGREEDY</pre>The PCRE2_UNGREEDY option is set when the regular expression is passed forcompilation to the native function. Note that REG_UNGREEDY is not part of thePOSIX standard.<pre> REG_UTF</pre>The PCRE2_UTF option is set when the regular expression is passed forcompilation to the native function. This causes the pattern itself and all datastrings used for matching it to be treated as UTF-8 strings. Note that REG_UTFis not part of the POSIX standard.</P><P>In the absence of these flags, no options are passed to the native function.This means that the regex is compiled with PCRE2 default semantics. Inparticular, the way it handles newline characters in the subject string is thePerl way, not the POSIX way. Note that setting PCRE2_MULTILINE has only<i>some</i> of the effects specified for REG_NEWLINE. It does not affect the waynewlines are matched by the dot metacharacter (they are not) or by a negativeclass such as [^a] (they are).</P><P>The yield of <b>pcre2_regcomp()</b> is zero on success, and non-zero otherwise.The <i>preg</i> structure is filled in on success, and one other member of thestructure (as well as <i>re_endp</i>) is public: <i>re_nsub</i> contains thenumber of capturing subpatterns in the regular expression. Various error codesare defined in the header file.</P><P>NOTE: If the yield of <b>pcre2_regcomp()</b> is non-zero, you must not attemptto use the contents of the <i>preg</i> structure. If, for example, you pass itto <b>pcre2_regexec()</b>, the result is undefined and your program is likely tocrash.</P><br><a name="SEC5" href="#TOC1">MATCHING NEWLINE CHARACTERS</a><br><P>This area is not simple, because POSIX and Perl take different views of things.It is not possible to get PCRE2 to obey POSIX semantics, but then PCRE2 wasnever intended to be a POSIX engine. The following table lists the differentpossibilities for matching newline characters in Perl and PCRE2:<pre> Default Change with
. matches newline no PCRE2_DOTALL newline matches [^a] yes not changeable $ matches \n at end yes PCRE2_DOLLAR_ENDONLY $ matches \n in middle no PCRE2_MULTILINE ^ matches \n in middle no PCRE2_MULTILINE</pre>This is the equivalent table for a POSIX-compatible pattern matcher:<pre> Default Change with
. matches newline yes REG_NEWLINE newline matches [^a] yes REG_NEWLINE $ matches \n at end no REG_NEWLINE $ matches \n in middle no REG_NEWLINE ^ matches \n in middle no REG_NEWLINE</pre>This behaviour is not what happens when PCRE2 is called via its POSIXAPI. By default, PCRE2's behaviour is the same as Perl's, except that there isno equivalent for PCRE2_DOLLAR_ENDONLY in Perl. In both PCRE2 and Perl, thereis no way to stop newline from matching [^a].</P><P>Default POSIX newline handling can be obtained by setting PCRE2_DOTALL andPCRE2_DOLLAR_ENDONLY when calling <b>pcre2_compile()</b> directly, but there isno way to make PCRE2 behave exactly as for the REG_NEWLINE action. When usingthe POSIX API, passing REG_NEWLINE to PCRE2's <b>pcre2_regcomp()</b> functioncauses PCRE2_MULTILINE to be passed to <b>pcre2_compile()</b>, and REG_DOTALLpasses PCRE2_DOTALL. There is no way to pass PCRE2_DOLLAR_ENDONLY.</P><br><a name="SEC6" href="#TOC1">MATCHING A PATTERN</a><br><P>The function <b>pcre2_regexec()</b> is called to match a compiled pattern<i>preg</i> against a given <i>string</i>, which is by default terminated by azero byte (but see REG_STARTEND below), subject to the options in <i>eflags</i>.These can be:<pre> REG_NOTBOL</pre>The PCRE2_NOTBOL option is set when calling the underlying PCRE2 matchingfunction.<pre> REG_NOTEMPTY</pre>The PCRE2_NOTEMPTY option is set when calling the underlying PCRE2 matchingfunction. Note that REG_NOTEMPTY is not part of the POSIX standard. However,setting this option can give more POSIX-like behaviour in some situations.<pre> REG_NOTEOL</pre>The PCRE2_NOTEOL option is set when calling the underlying PCRE2 matchingfunction.<pre> REG_STARTEND</pre>When this option is set, the subject string starts at <i>string</i> +<i>pmatch[0].rm_so</i> and ends at <i>string</i> + <i>pmatch[0].rm_eo</i>, whichshould point to the first character beyond the string. There may be binaryzeros within the subject string, and indeed, using REG_STARTEND is the onlyway to pass a subject string that contains a binary zero.</P><P>Whatever the value of <i>pmatch[0].rm_so</i>, the offsets of the matched stringand any captured substrings are still given relative to the start of<i>string</i> itself. (Before PCRE2 release 10.30 these were given relative to<i>string</i> + <i>pmatch[0].rm_so</i>, but this differs from otherimplementations.)</P><P>This is a BSD extension, compatible with but not specified by IEEE Standard1003.2 (POSIX.2), and should be used with caution in software intended to beportable to other systems. Note that a non-zero <i>rm_so</i> does not implyREG_NOTBOL; REG_STARTEND affects only the location and length of the string,not how it is matched. Setting REG_STARTEND and passing <i>pmatch</i> as NULLare mutually exclusive; the error REG_INVARG is returned.</P><P>If the pattern was compiled with the REG_NOSUB flag, no data about any matchedstrings is returned. The <i>nmatch</i> and <i>pmatch</i> arguments of<b>pcre2_regexec()</b> are ignored (except possibly as input for REG_STARTEND).</P><P>The value of <i>nmatch</i> may be zero, and the value <i>pmatch</i> may be NULL(unless REG_STARTEND is set); in both these cases no data about any matchedstrings is returned.</P><P>Otherwise, the portion of the string that was matched, and also any capturedsubstrings, are returned via the <i>pmatch</i> argument, which points to anarray of <i>nmatch</i> structures of type <i>regmatch_t</i>, containing themembers <i>rm_so</i> and <i>rm_eo</i>. These contain the byte offset to the firstcharacter of each substring and the offset to the first character after the endof each substring, respectively. The 0th element of the vector relates to theentire portion of <i>string</i> that was matched; subsequent elements relate tothe capturing subpatterns of the regular expression. Unused entries in thearray have both structure members set to -1.</P><P><i>regmatch_t</i> as well as the <i>regoff_t</i> typedef it uses are defined in<b>pcre2posix.h</b> and are not warranted to have the same size or layout as othersimilarly named types from other libraries that provide POSIX-style matching.</P><P>A successful match yields a zero return; various error codes are defined in theheader file, of which REG_NOMATCH is the "expected" failure code.</P><br><a name="SEC7" href="#TOC1">ERROR MESSAGES</a><br><P>The <b>pcre2_regerror()</b> function maps a non-zero errorcode from either<b>pcre2_regcomp()</b> or <b>pcre2_regexec()</b> to a printable message. If<i>preg</i> is not NULL, the error should have arisen from the use of thatstructure. A message terminated by a binary zero is placed in <i>errbuf</i>. Ifthe buffer is too short, only the first <i>errbuf_size</i> - 1 characters of theerror message are used. The yield of the function is the size of buffer neededto hold the whole message, including the terminating zero. This value isgreater than <i>errbuf_size</i> if the message was truncated.</P><br><a name="SEC8" href="#TOC1">MEMORY USAGE</a><br><P>Compiling a regular expression causes memory to be allocated and associatedwith the <i>preg</i> structure. The function <b>pcre2_regfree()</b> frees allsuch memory, after which <i>preg</i> may no longer be used as a compiledexpression.</P><br><a name="SEC9" href="#TOC1">AUTHOR</a><br><P>Philip Hazel<br>Retired from University Computing Service<br>Cambridge, England.<br></P><br><a name="SEC10" href="#TOC1">REVISION</a><br><P>Last updated: 19 January 2024<br>Copyright © 1997-2024 University of Cambridge.<br><p>Return to the <a href="index.html">PCRE2 index page</a>.</p>
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