301 lines
13 KiB
HTML
301 lines
13 KiB
HTML
<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 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">COMPILING A PATTERN</a>
|
|
<li><a name="TOC4" href="#SEC4">MATCHING NEWLINE CHARACTERS</a>
|
|
<li><a name="TOC5" href="#SEC5">MATCHING A PATTERN</a>
|
|
<li><a name="TOC6" href="#SEC6">ERROR MESSAGES</a>
|
|
<li><a name="TOC7" href="#SEC7">MEMORY USAGE</a>
|
|
<li><a name="TOC8" href="#SEC8">AUTHOR</a>
|
|
<li><a name="TOC9" href="#SEC9">REVISION</a>
|
|
</ul>
|
|
<br><a name="SEC1" href="#TOC1">SYNOPSIS</a><br>
|
|
<P>
|
|
<b>#include <pcre2posix.h></b>
|
|
</P>
|
|
<P>
|
|
<b>int regcomp(regex_t *<i>preg</i>, const char *<i>pattern</i>,</b>
|
|
<b> int <i>cflags</i>);</b>
|
|
<br>
|
|
<br>
|
|
<b>int 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 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 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. See the
|
|
<a href="pcre2api.html"><b>pcre2api</b></a>
|
|
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>
|
|
<P>
|
|
The functions described here are just wrapper functions that ultimately call
|
|
the PCRE2 native API. Their prototypes are defined in the <b>pcre2posix.h</b>
|
|
header file, and on Unix systems the library itself is called
|
|
<b>libpcre2-posix.a</b>, so can be accessed by adding <b>-lpcre2-posix</b> to the
|
|
command for linking an application that uses them. Because the POSIX functions
|
|
call the native ones, it is also necessary to add <b>-lpcre2-8</b>.
|
|
</P>
|
|
<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.
|
|
</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 header for these functions is supplied as <b>pcre2posix.h</b> to avoid any
|
|
potential clash with other POSIX libraries. It can, of course, be renamed or
|
|
aliased as <b>regex.h</b>, which is the "correct" name. 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">COMPILING A PATTERN</a><br>
|
|
<P>
|
|
The function <b>regcomp()</b> 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 <i>pattern</i>. 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.
|
|
</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_NOSUB
|
|
</pre>
|
|
When a pattern that is compiled with this flag is passed to <b>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 back references.
|
|
<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>regcomp()</b> is zero on success, and non-zero otherwise. The
|
|
<i>preg</i> structure is filled in on success, and one member of the structure
|
|
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>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>regexec()</b>, the result is undefined and your program is likely to crash.
|
|
</P>
|
|
<br><a name="SEC4" 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>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="SEC5" href="#TOC1">MATCHING A PATTERN</a><br>
|
|
<P>
|
|
The function <b>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>
|
|
The string is considered to start at <i>string</i> + <i>pmatch[0].rm_so</i> and
|
|
to have a terminating NUL located at <i>string</i> + <i>pmatch[0].rm_eo</i>
|
|
(there need not actually be a NUL at that location), regardless of the value of
|
|
<i>nmatch</i>. 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 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>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="SEC6" href="#TOC1">ERROR MESSAGES</a><br>
|
|
<P>
|
|
The <b>regerror()</b> function maps a non-zero errorcode from either
|
|
<b>regcomp()</b> or <b>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="SEC7" 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>regfree()</b> frees all such
|
|
memory, after which <i>preg</i> may no longer be used as a compiled expression.
|
|
</P>
|
|
<br><a name="SEC8" href="#TOC1">AUTHOR</a><br>
|
|
<P>
|
|
Philip Hazel
|
|
<br>
|
|
University Computing Service
|
|
<br>
|
|
Cambridge, England.
|
|
<br>
|
|
</P>
|
|
<br><a name="SEC9" href="#TOC1">REVISION</a><br>
|
|
<P>
|
|
Last updated: 31 January 2016
|
|
<br>
|
|
Copyright © 1997-2016 University of Cambridge.
|
|
<br>
|
|
<p>
|
|
Return to the <a href="index.html">PCRE2 index page</a>.
|
|
</p>
|