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| <title>pcre2posix specification</title> |
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| <h1>pcre2posix man page</h1> |
| <p> |
| Return to the <a href="index.html">PCRE2 index page</a>. |
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| <p> |
| This page is part of the PCRE2 HTML documentation. It was generated |
| automatically 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 regular |
| expression 8-bit library. There are no POSIX-style wrappers for PCRE2's 16-bit |
| and 32-bit libraries. See the |
| <a href="pcre2api.html"><b>pcre2api</b></a> |
| documentation for a description of PCRE2's native API, which contains much |
| additional functionality. |
| </P> |
| <P> |
| The functions described here are wrapper functions that ultimately call the |
| PCRE2 native API. Their prototypes are defined in the <b>pcre2posix.h</b> header |
| file, and they all have unique names starting with <b>pcre2_</b>. However, the |
| <b>pcre2posix.h</b> header also contains macro definitions that convert the |
| standard POSIX names such <b>regcomp()</b> into <b>pcre2_regcomp()</b> etc. This |
| means that a program can use the usual POSIX names without running the risk of |
| accidentally linking with POSIX functions from a different library. |
| </P> |
| <P> |
| On Unix-like systems the PCRE2 POSIX library is called <b>libpcre2-posix</b>, so |
| can be accessed by adding <b>-lpcre2-posix</b> to the command for linking an |
| application. Because the POSIX functions call the native ones, it is also |
| necessary to add <b>-lpcre2-8</b>. |
| </P> |
| <P> |
| Although they were not defined as protypes in <b>pcre2posix.h</b>, releases |
| 10.33 to 10.36 of the library contained functions with the POSIX names |
| <b>regcomp()</b> etc. These simply passed their arguments to the PCRE2 |
| functions. These functions were provided for backwards compatibility with |
| earlier versions of PCRE2, which had only POSIX names. However, this has proved |
| troublesome in situations where a program links with several libraries, some of |
| which 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 POSIX |
| libraries. It can, of course, be renamed or aliased as <b>regex.h</b>, which is |
| the "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 returning |
| captured 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> |
| Those POSIX option bits that can reasonably be mapped to PCRE2 native options |
| have been implemented. In addition, the option REG_EXTENDED is defined with the |
| value zero. This has no effect, but since programs that are written to the |
| POSIX interface often use it, this makes it easier to slot in PCRE2 as a |
| replacement library. Other POSIX options are not even defined. |
| </P> |
| <P> |
| There are also some options that are not defined by POSIX. These have been |
| added at the request of users who want to make use of certain PCRE2-specific |
| features 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-like |
| in style. The syntax and semantics of the regular expressions themselves are |
| still those of Perl, subject to the setting of various PCRE2 options, as |
| described below. "POSIX-like in style" means that the API approximates to the |
| POSIX definition; it is not fully POSIX-compatible, and in multi-unit encoding |
| domains it is probably even less compatible. |
| </P> |
| <P> |
| The descriptions below use the actual names of the functions, but, as described |
| above, the standard POSIX names (without the <b>pcre2_</b> prefix) may also be |
| used. |
| </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 an |
| internal form. By default, the pattern is a C string terminated by a binary |
| zero (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 about |
| the compiled regular expression. (It is also used for input when REG_PEND is |
| set.) |
| </P> |
| <P> |
| The argument <i>cflags</i> is either zero, or contains one or more of the bits |
| defined by the following macros: |
| <pre> |
| REG_DOTALL |
| </pre> |
| The PCRE2_DOTALL option is set when the regular expression is passed for |
| compilation to the native function. Note that REG_DOTALL is not part of the |
| POSIX standard. |
| <pre> |
| REG_ICASE |
| </pre> |
| The PCRE2_CASELESS option is set when the regular expression is passed for |
| compilation to the native function. |
| <pre> |
| REG_NEWLINE |
| </pre> |
| The PCRE2_MULTILINE option is set when the regular expression is passed for |
| compilation to the native function. Note that this does <i>not</i> mimic the |
| defined 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 for |
| compilation to the native function. This disables all meta characters in the |
| pattern, causing it to be treated as a literal string. The only other options |
| that are allowed with REG_NOSPEC are REG_ICASE, REG_NOSUB, REG_PEND, and |
| REG_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> arguments |
| are ignored, and no captured strings are returned. Versions of the PCRE library |
| prior to 10.22 used to set the PCRE2_NO_AUTO_CAPTURE compile option, but this |
| no 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 beyond |
| the end of the pattern before calling <b>pcre2_regcomp()</b>. The pattern itself |
| may now contain binary zeros, which are treated as data characters. Without |
| REG_PEND, a binary zero terminates the pattern and the <b>re_endp</b> field is |
| ignored. This is a GNU extension to the POSIX standard and should be used with |
| caution 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 for |
| compilation to the native function. This causes PCRE2 to use Unicode properties |
| when matchine \d, \w, etc., instead of just recognizing ASCII values. Note |
| that 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 for |
| compilation to the native function. Note that REG_UNGREEDY is not part of the |
| POSIX standard. |
| <pre> |
| REG_UTF |
| </pre> |
| The PCRE2_UTF option is set when the regular expression is passed for |
| compilation to the native function. This causes the pattern itself and all data |
| strings used for matching it to be treated as UTF-8 strings. Note that REG_UTF |
| is not part of the POSIX standard. |
| </P> |
| <P> |
| In the absence of these flags, no options are passed to the native function. |
| This means the the regex is compiled with PCRE2 default semantics. In |
| particular, the way it handles newline characters in the subject string is the |
| Perl 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 way |
| newlines are matched by the dot metacharacter (they are not) or by a negative |
| class 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 the |
| structure (as well as <i>re_endp</i>) is public: <i>re_nsub</i> contains the |
| number of capturing subpatterns in the regular expression. Various error codes |
| are defined in the header file. |
| </P> |
| <P> |
| NOTE: If the yield of <b>pcre2_regcomp()</b> is non-zero, you must not attempt |
| to use the contents of the <i>preg</i> structure. If, for example, you pass it |
| to <b>pcre2_regexec()</b>, the result is undefined and your program is likely to |
| crash. |
| </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 was |
| never intended to be a POSIX engine. The following table lists the different |
| possibilities 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 POSIX |
| API. By default, PCRE2's behaviour is the same as Perl's, except that there is |
| no equivalent for PCRE2_DOLLAR_ENDONLY in Perl. In both PCRE2 and Perl, there |
| is no way to stop newline from matching [^a]. |
| </P> |
| <P> |
| Default POSIX newline handling can be obtained by setting PCRE2_DOTALL and |
| PCRE2_DOLLAR_ENDONLY when calling <b>pcre2_compile()</b> directly, but there is |
| no way to make PCRE2 behave exactly as for the REG_NEWLINE action. When using |
| the POSIX API, passing REG_NEWLINE to PCRE2's <b>pcre2_regcomp()</b> function |
| causes PCRE2_MULTILINE to be passed to <b>pcre2_compile()</b>, and REG_DOTALL |
| passes 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 a |
| zero 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 matching |
| function. |
| <pre> |
| REG_NOTEMPTY |
| </pre> |
| The PCRE2_NOTEMPTY option is set when calling the underlying PCRE2 matching |
| function. 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 matching |
| function. |
| <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>, which |
| should point to the first character beyond the string. There may be binary |
| zeros within the subject string, and indeed, using REG_STARTEND is the only |
| way 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 string |
| and 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 other |
| implementations.) |
| </P> |
| <P> |
| This is a BSD extension, compatible with but not specified by IEEE Standard |
| 1003.2 (POSIX.2), and should be used with caution in software intended to be |
| portable to other systems. Note that a non-zero <i>rm_so</i> does not imply |
| REG_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 NULL |
| are mutually exclusive; the error REG_INVARG is returned. |
| </P> |
| <P> |
| If the pattern was compiled with the REG_NOSUB flag, no data about any matched |
| strings 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 matched |
| strings is returned. |
| </P> |
| <P> |
| Otherwise, the portion of the string that was matched, and also any captured |
| substrings, are returned via the <i>pmatch</i> argument, which points to an |
| array of <i>nmatch</i> structures of type <i>regmatch_t</i>, containing the |
| members <i>rm_so</i> and <i>rm_eo</i>. These contain the byte offset to the first |
| character of each substring and the offset to the first character after the end |
| of each substring, respectively. The 0th element of the vector relates to the |
| entire portion of <i>string</i> that was matched; subsequent elements relate to |
| the capturing subpatterns of the regular expression. Unused entries in the |
| array have both structure members set to -1. |
| </P> |
| <P> |
| A successful match yields a zero return; various error codes are defined in the |
| header 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 that |
| structure. A message terminated by a binary zero is placed in <i>errbuf</i>. If |
| the buffer is too short, only the first <i>errbuf_size</i> - 1 characters of the |
| error message are used. The yield of the function is the size of buffer needed |
| to hold the whole message, including the terminating zero. This value is |
| greater 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 associated |
| with the <i>preg</i> structure. The function <b>pcre2_regfree()</b> frees all |
| such memory, after which <i>preg</i> may no longer be used as a compiled |
| expression. |
| </P> |
| <br><a name="SEC9" href="#TOC1">AUTHOR</a><br> |
| <P> |
| Philip Hazel |
| <br> |
| University Computing Service |
| <br> |
| Cambridge, England. |
| <br> |
| </P> |
| <br><a name="SEC10" href="#TOC1">REVISION</a><br> |
| <P> |
| Last updated: 26 April 2021 |
| <br> |
| Copyright © 1997-2021 University of Cambridge. |
| <br> |
| <p> |
| Return to the <a href="index.html">PCRE2 index page</a>. |
| </p> |