| .TH PCREPOSIX 3 |
| .SH NAME |
| PCRE - Perl-compatible regular expressions. |
| .SH "SYNOPSIS OF POSIX API" |
| .rs |
| .sp |
| .B #include <pcreposix.h> |
| .PP |
| .SM |
| .B int regcomp(regex_t *\fIpreg\fP, const char *\fIpattern\fP, |
| .ti +5n |
| .B int \fIcflags\fP); |
| .PP |
| .B int regexec(regex_t *\fIpreg\fP, const char *\fIstring\fP, |
| .ti +5n |
| .B size_t \fInmatch\fP, regmatch_t \fIpmatch\fP[], int \fIeflags\fP); |
| .PP |
| .B size_t regerror(int \fIerrcode\fP, const regex_t *\fIpreg\fP, |
| .ti +5n |
| .B char *\fIerrbuf\fP, size_t \fIerrbuf_size\fP); |
| .PP |
| .B void regfree(regex_t *\fIpreg\fP); |
| . |
| .SH DESCRIPTION |
| .rs |
| .sp |
| This set of functions provides a POSIX-style API to the PCRE regular expression |
| package. See the |
| .\" HREF |
| \fBpcreapi\fP |
| .\" |
| documentation for a description of PCRE's native API, which contains much |
| additional functionality. |
| .P |
| The functions described here are just wrapper functions that ultimately call |
| the PCRE native API. Their prototypes are defined in the \fBpcreposix.h\fP |
| header file, and on Unix systems the library itself is called |
| \fBpcreposix.a\fP, so can be accessed by adding \fB-lpcreposix\fP to the |
| command for linking an application that uses them. Because the POSIX functions |
| call the native ones, it is also necessary to add \fB-lpcre\fP. |
| .P |
| I have implemented only those POSIX option bits that can be reasonably mapped |
| to PCRE native options. 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 PCRE as a |
| replacement library. Other POSIX options are not even defined. |
| .P |
| There are also some other options that are not defined by POSIX. These have |
| been added at the request of users who want to make use of certain |
| PCRE-specific features via the POSIX calling interface. |
| .P |
| When PCRE 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 PCRE 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-byte encoding |
| domains it is probably even less compatible. |
| .P |
| The header for these functions is supplied as \fBpcreposix.h\fP to avoid any |
| potential clash with other POSIX libraries. It can, of course, be renamed or |
| aliased as \fBregex.h\fP, which is the "correct" name. It provides two |
| structure types, \fIregex_t\fP for compiled internal forms, and |
| \fIregmatch_t\fP for returning captured substrings. It also defines some |
| constants whose names start with "REG_"; these are used for setting options and |
| identifying error codes. |
| . |
| . |
| .SH "COMPILING A PATTERN" |
| .rs |
| .sp |
| The function \fBregcomp()\fP is called to compile a pattern into an |
| internal form. The pattern is a C string terminated by a binary zero, and |
| is passed in the argument \fIpattern\fP. The \fIpreg\fP argument is a pointer |
| to a \fBregex_t\fP structure that is used as a base for storing information |
| about the compiled regular expression. |
| .P |
| The argument \fIcflags\fP is either zero, or contains one or more of the bits |
| defined by the following macros: |
| .sp |
| REG_DOTALL |
| .sp |
| The PCRE_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. |
| .sp |
| REG_ICASE |
| .sp |
| The PCRE_CASELESS option is set when the regular expression is passed for |
| compilation to the native function. |
| .sp |
| REG_NEWLINE |
| .sp |
| The PCRE_MULTILINE option is set when the regular expression is passed for |
| compilation to the native function. Note that this does \fInot\fP mimic the |
| defined POSIX behaviour for REG_NEWLINE (see the following section). |
| .sp |
| REG_NOSUB |
| .sp |
| The PCRE_NO_AUTO_CAPTURE option is set when the regular expression is passed |
| for compilation to the native function. In addition, when a pattern that is |
| compiled with this flag is passed to \fBregexec()\fP for matching, the |
| \fInmatch\fP and \fIpmatch\fP arguments are ignored, and no captured strings |
| are returned. |
| .sp |
| REG_UCP |
| .sp |
| The PCRE_UCP option is set when the regular expression is passed for |
| compilation to the native function. This causes PCRE to use Unicode properties |
| when matchine \ed, \ew, etc., instead of just recognizing ASCII values. Note |
| that REG_UTF8 is not part of the POSIX standard. |
| .sp |
| REG_UNGREEDY |
| .sp |
| The PCRE_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. |
| .sp |
| REG_UTF8 |
| .sp |
| The PCRE_UTF8 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_UTF8 |
| is not part of the POSIX standard. |
| .P |
| In the absence of these flags, no options are passed to the native function. |
| This means the the regex is compiled with PCRE 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 PCRE_MULTILINE has only |
| \fIsome\fP of the effects specified for REG_NEWLINE. It does not affect the way |
| newlines are matched by . (they are not) or by a negative class such as [^a] |
| (they are). |
| .P |
| The yield of \fBregcomp()\fP is zero on success, and non-zero otherwise. The |
| \fIpreg\fP structure is filled in on success, and one member of the structure |
| is public: \fIre_nsub\fP contains the number of capturing subpatterns in |
| the regular expression. Various error codes are defined in the header file. |
| .P |
| NOTE: If the yield of \fBregcomp()\fP is non-zero, you must not attempt to |
| use the contents of the \fIpreg\fP structure. If, for example, you pass it to |
| \fBregexec()\fP, the result is undefined and your program is likely to crash. |
| . |
| . |
| .SH "MATCHING NEWLINE CHARACTERS" |
| .rs |
| .sp |
| This area is not simple, because POSIX and Perl take different views of things. |
| It is not possible to get PCRE to obey POSIX semantics, but then PCRE was never |
| intended to be a POSIX engine. The following table lists the different |
| possibilities for matching newline characters in PCRE: |
| .sp |
| Default Change with |
| .sp |
| . matches newline no PCRE_DOTALL |
| newline matches [^a] yes not changeable |
| $ matches \en at end yes PCRE_DOLLARENDONLY |
| $ matches \en in middle no PCRE_MULTILINE |
| ^ matches \en in middle no PCRE_MULTILINE |
| .sp |
| This is the equivalent table for POSIX: |
| .sp |
| Default Change with |
| .sp |
| . matches newline yes REG_NEWLINE |
| newline matches [^a] yes REG_NEWLINE |
| $ matches \en at end no REG_NEWLINE |
| $ matches \en in middle no REG_NEWLINE |
| ^ matches \en in middle no REG_NEWLINE |
| .sp |
| PCRE's behaviour is the same as Perl's, except that there is no equivalent for |
| PCRE_DOLLAR_ENDONLY in Perl. In both PCRE and Perl, there is no way to stop |
| newline from matching [^a]. |
| .P |
| The default POSIX newline handling can be obtained by setting PCRE_DOTALL and |
| PCRE_DOLLAR_ENDONLY, but there is no way to make PCRE behave exactly as for the |
| REG_NEWLINE action. |
| . |
| . |
| .SH "MATCHING A PATTERN" |
| .rs |
| .sp |
| The function \fBregexec()\fP is called to match a compiled pattern \fIpreg\fP |
| against a given \fIstring\fP, which is by default terminated by a zero byte |
| (but see REG_STARTEND below), subject to the options in \fIeflags\fP. These can |
| be: |
| .sp |
| REG_NOTBOL |
| .sp |
| The PCRE_NOTBOL option is set when calling the underlying PCRE matching |
| function. |
| .sp |
| REG_NOTEMPTY |
| .sp |
| The PCRE_NOTEMPTY option is set when calling the underlying PCRE 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. |
| .sp |
| REG_NOTEOL |
| .sp |
| The PCRE_NOTEOL option is set when calling the underlying PCRE matching |
| function. |
| .sp |
| REG_STARTEND |
| .sp |
| The string is considered to start at \fIstring\fP + \fIpmatch[0].rm_so\fP and |
| to have a terminating NUL located at \fIstring\fP + \fIpmatch[0].rm_eo\fP |
| (there need not actually be a NUL at that location), regardless of the value of |
| \fInmatch\fP. 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 \fIrm_so\fP does |
| not imply REG_NOTBOL; REG_STARTEND affects only the location of the string, not |
| how it is matched. |
| .P |
| If the pattern was compiled with the REG_NOSUB flag, no data about any matched |
| strings is returned. The \fInmatch\fP and \fIpmatch\fP arguments of |
| \fBregexec()\fP are ignored. |
| .P |
| If the value of \fInmatch\fP is zero, or if the value \fIpmatch\fP is NULL, |
| no data about any matched strings is returned. |
| .P |
| Otherwise,the portion of the string that was matched, and also any captured |
| substrings, are returned via the \fIpmatch\fP argument, which points to an |
| array of \fInmatch\fP structures of type \fIregmatch_t\fP, containing the |
| members \fIrm_so\fP and \fIrm_eo\fP. These contain the 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 \fIstring\fP 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 |
| 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. |
| . |
| . |
| .SH "ERROR MESSAGES" |
| .rs |
| .sp |
| The \fBregerror()\fP function maps a non-zero errorcode from either |
| \fBregcomp()\fP or \fBregexec()\fP to a printable message. If \fIpreg\fP is not |
| NULL, the error should have arisen from the use of that structure. A message |
| terminated by a binary zero is placed in \fIerrbuf\fP. The length of the |
| message, including the zero, is limited to \fIerrbuf_size\fP. The yield of the |
| function is the size of buffer needed to hold the whole message. |
| . |
| . |
| .SH MEMORY USAGE |
| .rs |
| .sp |
| Compiling a regular expression causes memory to be allocated and associated |
| with the \fIpreg\fP structure. The function \fBregfree()\fP frees all such |
| memory, after which \fIpreg\fP may no longer be used as a compiled expression. |
| . |
| . |
| .SH AUTHOR |
| .rs |
| .sp |
| .nf |
| Philip Hazel |
| University Computing Service |
| Cambridge CB2 3QH, England. |
| .fi |
| . |
| . |
| .SH REVISION |
| .rs |
| .sp |
| .nf |
| Last updated: 16 May 2010 |
| Copyright (c) 1997-2010 University of Cambridge. |
| .fi |