| .TH PCRE2POSIX 3 "30 January 2019" "PCRE2 10.33" |
| .SH NAME |
| PCRE2 - Perl-compatible regular expressions (revised API) |
| .SH "SYNOPSIS" |
| .rs |
| .sp |
| .B #include <pcre2posix.h> |
| .PP |
| .nf |
| .B int pcre2_regcomp(regex_t *\fIpreg\fP, const char *\fIpattern\fP, |
| .B " int \fIcflags\fP);" |
| .sp |
| .B int pcre2_regexec(const regex_t *\fIpreg\fP, const char *\fIstring\fP, |
| .B " size_t \fInmatch\fP, regmatch_t \fIpmatch\fP[], int \fIeflags\fP);" |
| .sp |
| .B "size_t pcre2_regerror(int \fIerrcode\fP, const regex_t *\fIpreg\fP," |
| .B " char *\fIerrbuf\fP, size_t \fIerrbuf_size\fP);" |
| .sp |
| .B void pcre2_regfree(regex_t *\fIpreg\fP); |
| .fi |
| . |
| .SH DESCRIPTION |
| .rs |
| .sp |
| 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 |
| .\" HREF |
| \fBpcre2api\fP |
| .\" |
| documentation for a description of PCRE2's native API, which contains much |
| additional functionality. |
| .P |
| The functions described here are wrapper functions that ultimately call the |
| PCRE2 native API. Their prototypes are defined in the \fBpcre2posix.h\fP header |
| file, and they all have unique names starting with \fBpcre2_\fP. However, the |
| \fBpcre2posix.h\fP header also contains macro definitions that convert the |
| standard POSIX names such \fBregcomp()\fP into \fBpcre2_regcomp()\fP 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 |
| On Unix-like systems the PCRE2 POSIX library is called \fBlibpcre2-posix\fP, so |
| can be accessed by adding \fB-lpcre2-posix\fP to the command for linking an |
| application. Because the POSIX functions call the native ones, it is also |
| necessary to add \fB-lpcre2-8\fP. |
| .P |
| Although they are not defined as protypes in \fBpcre2posix.h\fP, the library |
| does contain functions with the POSIX names \fBregcomp()\fP etc. These simply |
| pass their arguments to the PCRE2 functions. These functions are provided for |
| backwards compatibility with earlier versions of PCRE2, so that existing |
| programs do not have to be recompiled. |
| .P |
| Calling the header file \fBpcre2posix.h\fP avoids any conflict with other POSIX |
| libraries. It can, of course, be renamed or aliased as \fBregex.h\fP, which is |
| the "correct" name, if there is no clash. 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 "USING THE POSIX FUNCTIONS" |
| .rs |
| .sp |
| 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 |
| 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 |
| 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 |
| The descriptions below use the actual names of the functions, but, as described |
| above, the standard POSIX names (without the \fBpcre2_\fP prefix) may also be |
| used. |
| . |
| . |
| .SH "COMPILING A PATTERN" |
| .rs |
| .sp |
| The function \fBpcre2_regcomp()\fP 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 \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. (It is also used for input when REG_PEND is |
| set.) |
| .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 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. |
| .sp |
| REG_ICASE |
| .sp |
| The PCRE2_CASELESS option is set when the regular expression is passed for |
| compilation to the native function. |
| .sp |
| REG_NEWLINE |
| .sp |
| The PCRE2_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_NOSPEC |
| .sp |
| 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. |
| .sp |
| REG_NOSUB |
| .sp |
| When a pattern that is compiled with this flag is passed to |
| \fBpcre2_regexec()\fP for matching, the \fInmatch\fP and \fIpmatch\fP 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. |
| .sp |
| REG_PEND |
| .sp |
| If this option is set, the \fBreg_endp\fP field in the \fIpreg\fP structure |
| (which has the type const char *) must be set to point to the character beyond |
| the end of the pattern before calling \fBpcre2_regcomp()\fP. 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 \fBre_endp\fP 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. |
| .sp |
| REG_UCP |
| .sp |
| 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 \ed, \ew, etc., instead of just recognizing ASCII values. Note |
| that REG_UCP is not part of the POSIX standard. |
| .sp |
| REG_UNGREEDY |
| .sp |
| 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. |
| .sp |
| REG_UTF |
| .sp |
| 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 |
| 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 |
| \fIsome\fP 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 |
| The yield of \fBpcre2_regcomp()\fP is zero on success, and non-zero otherwise. |
| The \fIpreg\fP structure is filled in on success, and one other member of the |
| structure (as well as \fIre_endp\fP) 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 \fBpcre2_regcomp()\fP is non-zero, you must not attempt |
| to use the contents of the \fIpreg\fP structure. If, for example, you pass it |
| to \fBpcre2_regexec()\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 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: |
| .sp |
| Default Change with |
| .sp |
| . matches newline no PCRE2_DOTALL |
| newline matches [^a] yes not changeable |
| $ matches \en at end yes PCRE2_DOLLAR_ENDONLY |
| $ matches \en in middle no PCRE2_MULTILINE |
| ^ matches \en in middle no PCRE2_MULTILINE |
| .sp |
| This is the equivalent table for a POSIX-compatible pattern matcher: |
| .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 |
| 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 |
| Default POSIX newline handling can be obtained by setting PCRE2_DOTALL and |
| PCRE2_DOLLAR_ENDONLY when calling \fBpcre2_compile()\fP 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 \fBpcre2_regcomp()\fP function |
| causes PCRE2_MULTILINE to be passed to \fBpcre2_compile()\fP, and REG_DOTALL |
| passes PCRE2_DOTALL. There is no way to pass PCRE2_DOLLAR_ENDONLY. |
| . |
| . |
| .SH "MATCHING A PATTERN" |
| .rs |
| .sp |
| The function \fBpcre2_regexec()\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 PCRE2_NOTBOL option is set when calling the underlying PCRE2 matching |
| function. |
| .sp |
| REG_NOTEMPTY |
| .sp |
| 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. |
| .sp |
| REG_NOTEOL |
| .sp |
| The PCRE2_NOTEOL option is set when calling the underlying PCRE2 matching |
| function. |
| .sp |
| REG_STARTEND |
| .sp |
| When this option is set, the subject string starts at \fIstring\fP + |
| \fIpmatch[0].rm_so\fP and ends at \fIstring\fP + \fIpmatch[0].rm_eo\fP, 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 |
| Whatever the value of \fIpmatch[0].rm_so\fP, the offsets of the matched string |
| and any captured substrings are still given relative to the start of |
| \fIstring\fP itself. (Before PCRE2 release 10.30 these were given relative to |
| \fIstring\fP + \fIpmatch[0].rm_so\fP, but this differs from other |
| implementations.) |
| .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 \fIrm_so\fP 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 \fIpmatch\fP as NULL |
| are mutually exclusive; the error REG_INVARG is returned. |
| .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 |
| \fBpcre2_regexec()\fP are ignored (except possibly as input for REG_STARTEND). |
| .P |
| The value of \fInmatch\fP may be zero, and the value \fIpmatch\fP may be NULL |
| (unless REG_STARTEND is set); in both these cases 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 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 \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 \fBpcre2_regerror()\fP function maps a non-zero errorcode from either |
| \fBpcre2_regcomp()\fP or \fBpcre2_regexec()\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. If |
| the buffer is too short, only the first \fIerrbuf_size\fP - 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 \fIerrbuf_size\fP if the message was truncated. |
| . |
| . |
| .SH MEMORY USAGE |
| .rs |
| .sp |
| Compiling a regular expression causes memory to be allocated and associated |
| with the \fIpreg\fP structure. The function \fBpcre2_regfree()\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, England. |
| .fi |
| . |
| . |
| .SH REVISION |
| .rs |
| .sp |
| .nf |
| Last updated: 30 January 2019 |
| Copyright (c) 1997-2019 University of Cambridge. |
| .fi |