283 lines
12 KiB
Groff
283 lines
12 KiB
Groff
.TH PCRE2POSIX 3 "03 June 2017" "PCRE2 10.30"
|
|
.SH NAME
|
|
PCRE2 - Perl-compatible regular expressions (revised API)
|
|
.SH "SYNOPSIS"
|
|
.rs
|
|
.sp
|
|
.B #include <pcre2posix.h>
|
|
.PP
|
|
.nf
|
|
.B int regcomp(regex_t *\fIpreg\fP, const char *\fIpattern\fP,
|
|
.B " int \fIcflags\fP);"
|
|
.sp
|
|
.B int 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 regerror(int \fIerrcode\fP, const regex_t *\fIpreg\fP,"
|
|
.B " char *\fIerrbuf\fP, size_t \fIerrbuf_size\fP);"
|
|
.sp
|
|
.B void 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. See the
|
|
.\" HREF
|
|
\fBpcre2api\fP
|
|
.\"
|
|
documentation for a description of PCRE2's native API, which contains much
|
|
additional functionality. There are no POSIX-style wrappers for PCRE2's 16-bit
|
|
and 32-bit libraries.
|
|
.P
|
|
The functions described here are just wrapper functions that ultimately call
|
|
the PCRE2 native API. Their prototypes are defined in the \fBpcre2posix.h\fP
|
|
header file, and on Unix systems the library itself is called
|
|
\fBlibpcre2-posix.a\fP, so can be accessed by adding \fB-lpcre2-posix\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-lpcre2-8\fP.
|
|
.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
|
|
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.
|
|
.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 header for these functions is supplied as \fBpcre2posix.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 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_NOSUB
|
|
.sp
|
|
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. 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 back references.
|
|
.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 \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 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 \fBregcomp()\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 \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 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 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. However, the offsets of the matched
|
|
string and any captured substrings are still given relative to the start of
|
|
\fIstring\fP. (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 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
|
|
\fBregexec()\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 \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. 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 \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, England.
|
|
.fi
|
|
.
|
|
.
|
|
.SH REVISION
|
|
.rs
|
|
.sp
|
|
.nf
|
|
Last updated: 03 June 2017
|
|
Copyright (c) 1997-2017 University of Cambridge.
|
|
.fi
|