542 lines
16 KiB
Groff
542 lines
16 KiB
Groff
.\" Copyright (c) 1992, 1993, 1994 Henry Spencer.
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.\" Copyright (c) 1992, 1993, 1994
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" This code is derived from software contributed to Berkeley by
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.\" Henry Spencer.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)regex.3 8.4 (Berkeley) 3/20/94
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.\"
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.TH REGEX 3 "March 20, 1994"
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.de ZR
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.\" one other place knows this name: the SEE ALSO section
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.BR re_format (7) \\$1
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..
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.SH NAME
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regex, regcomp, regexec, regerror, regfree \- regular-expression library
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.SH SYNOPSIS
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.ft B
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.\".na
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#include <sys/types.h>
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.br
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#include <regex.h>
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.sp
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.in +.5i
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.ti -.5i
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int regcomp(regex_t *\fIpreg\fP, const char *\fIpattern\fP, int \fIcflags\fP);
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.ti -.5i
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int regexec(const regex_t *\fIpreg\fP, const char *\fIstring\fP,
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size_t \fInmatch\fP, regmatch_t \fIpmatch\fP[], int \fIeflags\fP);
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.ti -.5i
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size_t regerror(int \fIerrcode\fP, const regex_t *\fIpreg\fP,
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char *\fIerrbuf\fP, size_t \fIerrbuf_size\fP);
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.ti -.5i
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void regfree(regex_t *\fIpreg\fP);
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.in -.5i
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.ft R
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.SH DESCRIPTION
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These routines implement POSIX 1003.2 regular expressions (``RE''s);
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see
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.ZR .
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.B Regcomp
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compiles an RE written as a string into an internal form,
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.B regexec
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matches that internal form against a string and reports results,
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.B regerror
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transforms error codes from either into human-readable messages,
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and
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.B regfree
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frees any dynamically-allocated storage used by the internal form
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of an RE.
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.PP
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The header
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.I <regex.h>
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declares two structure types,
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.B regex_t
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and
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.BR regmatch_t ,
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the former for compiled internal forms and the latter for match reporting.
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It also declares the four functions,
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a type
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.BR regoff_t ,
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and a number of constants with names starting with ``REG_''.
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.PP
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.B Regcomp
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compiles the regular expression contained in the
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.I pattern
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string,
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subject to the flags in
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.IR cflags ,
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and places the results in the
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.B regex_t
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structure pointed to by
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.IR preg .
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.I Cflags
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is the bitwise OR of zero or more of the following flags:
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.IP REG_EXTENDED \w'REG_EXTENDED'u+2n
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Compile modern (``extended'') REs,
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rather than the obsolete (``basic'') REs that
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are the default.
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.IP REG_BASIC
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This is a synonym for 0,
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provided as a counterpart to REG_EXTENDED to improve readability.
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.IP REG_NOSPEC
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Compile with recognition of all special characters turned off.
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All characters are thus considered ordinary,
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so the ``RE'' is a literal string.
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This is an extension,
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compatible with but not specified by POSIX 1003.2,
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and should be used with
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caution in software intended to be portable to other systems.
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REG_EXTENDED and REG_NOSPEC may not be used
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in the same call to
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.IR regcomp .
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.IP REG_ICASE
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Compile for matching that ignores upper/lower case distinctions.
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See
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.ZR .
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.IP REG_NOSUB
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Compile for matching that need only report success or failure,
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not what was matched.
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.IP REG_NEWLINE
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Compile for newline-sensitive matching.
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By default, newline is a completely ordinary character with no special
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meaning in either REs or strings.
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With this flag,
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`[^' bracket expressions and `.' never match newline,
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a `^' anchor matches the null string after any newline in the string
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in addition to its normal function,
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and the `$' anchor matches the null string before any newline in the
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string in addition to its normal function.
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.IP REG_PEND
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The regular expression ends,
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not at the first NUL,
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but just before the character pointed to by the
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.B re_endp
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member of the structure pointed to by
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.IR preg .
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The
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.B re_endp
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member is of type
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.BR "const\ char\ *" .
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This flag permits inclusion of NULs in the RE;
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they are considered ordinary characters.
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This is an extension,
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compatible with but not specified by POSIX 1003.2,
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and should be used with
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caution in software intended to be portable to other systems.
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.PP
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When successful,
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.B regcomp
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returns 0 and fills in the structure pointed to by
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.IR preg .
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One member of that structure
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(other than
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.BR re_endp )
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is publicized:
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.BR re_nsub ,
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of type
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.BR size_t ,
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contains the number of parenthesized subexpressions within the RE
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(except that the value of this member is undefined if the
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REG_NOSUB flag was used).
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If
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.B regcomp
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fails, it returns a non-zero error code;
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see DIAGNOSTICS.
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.PP
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.B Regexec
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matches the compiled RE pointed to by
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.I preg
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against the
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.IR string ,
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subject to the flags in
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.IR eflags ,
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and reports results using
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.IR nmatch ,
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.IR pmatch ,
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and the returned value.
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The RE must have been compiled by a previous invocation of
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.BR regcomp .
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The compiled form is not altered during execution of
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.BR regexec ,
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so a single compiled RE can be used simultaneously by multiple threads.
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.PP
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By default,
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the NUL-terminated string pointed to by
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.I string
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is considered to be the text of an entire line, minus any terminating
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newline.
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The
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.I eflags
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argument is the bitwise OR of zero or more of the following flags:
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.IP REG_NOTBOL \w'REG_STARTEND'u+2n
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The first character of
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the string
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is not the beginning of a line, so the `^' anchor should not match before it.
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This does not affect the behavior of newlines under REG_NEWLINE.
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.IP REG_NOTEOL
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The NUL terminating
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the string
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does not end a line, so the `$' anchor should not match before it.
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This does not affect the behavior of newlines under REG_NEWLINE.
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.IP REG_STARTEND
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The string is considered to start at
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\fIstring\fR\ + \fIpmatch\fR[0].\fBrm_so\fR
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and to have a terminating NUL located at
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\fIstring\fR\ + \fIpmatch\fR[0].\fBrm_eo\fR
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(there need not actually be a NUL at that location),
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regardless of the value of
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.IR nmatch .
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See below for the definition of
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.IR pmatch
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and
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.IR nmatch .
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This is an extension,
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compatible with but not specified by POSIX 1003.2,
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and should be used with
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caution in software intended to be portable to other systems.
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Note that a non-zero \fBrm_so\fR does not imply REG_NOTBOL;
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REG_STARTEND affects only the location of the string,
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not how it is matched.
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.PP
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See
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.ZR
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for a discussion of what is matched in situations where an RE or a
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portion thereof could match any of several substrings of
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.IR string .
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.PP
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Normally,
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.B regexec
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returns 0 for success and the non-zero code REG_NOMATCH for failure.
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Other non-zero error codes may be returned in exceptional situations;
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see DIAGNOSTICS.
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.PP
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If REG_NOSUB was specified in the compilation of the RE,
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or if
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.I nmatch
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is 0,
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.B regexec
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ignores the
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.I pmatch
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argument (but see below for the case where REG_STARTEND is specified).
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Otherwise,
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.I pmatch
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points to an array of
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.I nmatch
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structures of type
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.BR regmatch_t .
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Such a structure has at least the members
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.B rm_so
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and
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.BR rm_eo ,
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both of type
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.B regoff_t
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(a signed arithmetic type at least as large as an
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.B off_t
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and a
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.BR ssize_t ),
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containing respectively the offset of the first character of a substring
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and the offset of the first character after the end of the substring.
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Offsets are measured from the beginning of the
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.I string
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argument given to
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.BR regexec .
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An empty substring is denoted by equal offsets,
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both indicating the character following the empty substring.
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.PP
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The 0th member of the
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.I pmatch
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array is filled in to indicate what substring of
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.I string
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was matched by the entire RE.
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Remaining members report what substring was matched by parenthesized
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subexpressions within the RE;
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member
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.I i
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reports subexpression
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.IR i ,
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with subexpressions counted (starting at 1) by the order of their opening
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parentheses in the RE, left to right.
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Unused entries in the array\(emcorresponding either to subexpressions that
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did not participate in the match at all, or to subexpressions that do not
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exist in the RE (that is, \fIi\fR\ > \fIpreg\fR\->\fBre_nsub\fR)\(emhave both
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.B rm_so
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and
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.B rm_eo
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set to \-1.
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If a subexpression participated in the match several times,
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the reported substring is the last one it matched.
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(Note, as an example in particular, that when the RE `(b*)+' matches `bbb',
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the parenthesized subexpression matches each of the three `b's and then
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an infinite number of empty strings following the last `b',
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so the reported substring is one of the empties.)
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.PP
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If REG_STARTEND is specified,
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.I pmatch
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must point to at least one
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.B regmatch_t
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(even if
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.I nmatch
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is 0 or REG_NOSUB was specified),
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to hold the input offsets for REG_STARTEND.
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Use for output is still entirely controlled by
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.IR nmatch ;
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if
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.I nmatch
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is 0 or REG_NOSUB was specified,
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the value of
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.IR pmatch [0]
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will not be changed by a successful
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.BR regexec .
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.PP
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.B Regerror
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maps a non-zero
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.I errcode
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from either
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.B regcomp
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or
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.B regexec
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to a human-readable, printable message.
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If
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.I preg
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is non-NULL,
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the error code should have arisen from use of
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the
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.B regex_t
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pointed to by
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.IR preg ,
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and if the error code came from
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.BR regcomp ,
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it should have been the result from the most recent
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.B regcomp
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using that
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.BR regex_t .
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.RI ( Regerror
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may be able to supply a more detailed message using information
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from the
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.BR regex_t .)
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.B Regerror
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places the NUL-terminated message into the buffer pointed to by
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.IR errbuf ,
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limiting the length (including the NUL) to at most
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.I errbuf_size
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bytes.
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If the whole message won't fit,
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as much of it as will fit before the terminating NUL is supplied.
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In any case,
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the returned value is the size of buffer needed to hold the whole
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message (including terminating NUL).
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If
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.I errbuf_size
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is 0,
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.I errbuf
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is ignored but the return value is still correct.
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.PP
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If the
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.I errcode
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given to
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.B regerror
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is first ORed with REG_ITOA,
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the ``message'' that results is the printable name of the error code,
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e.g. ``REG_NOMATCH'',
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rather than an explanation thereof.
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If
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.I errcode
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is REG_ATOI,
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then
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.I preg
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shall be non-NULL and the
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.B re_endp
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member of the structure it points to
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must point to the printable name of an error code;
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in this case, the result in
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.I errbuf
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is the decimal digits of
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the numeric value of the error code
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(0 if the name is not recognized).
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REG_ITOA and REG_ATOI are intended primarily as debugging facilities;
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they are extensions,
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compatible with but not specified by POSIX 1003.2,
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and should be used with
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caution in software intended to be portable to other systems.
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Be warned also that they are considered experimental and changes are possible.
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.PP
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.B Regfree
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frees any dynamically-allocated storage associated with the compiled RE
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pointed to by
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.IR preg .
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The remaining
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.B regex_t
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is no longer a valid compiled RE
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and the effect of supplying it to
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.B regexec
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or
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.B regerror
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is undefined.
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.PP
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None of these functions references global variables except for tables
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of constants;
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all are safe for use from multiple threads if the arguments are safe.
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.SH IMPLEMENTATION CHOICES
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There are a number of decisions that 1003.2 leaves up to the implementor,
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either by explicitly saying ``undefined'' or by virtue of them being
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forbidden by the RE grammar.
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This implementation treats them as follows.
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.PP
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See
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.ZR
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for a discussion of the definition of case-independent matching.
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.PP
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There is no particular limit on the length of REs,
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except insofar as memory is limited.
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Memory usage is approximately linear in RE size, and largely insensitive
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to RE complexity, except for bounded repetitions.
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See BUGS for one short RE using them
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that will run almost any system out of memory.
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.PP
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A backslashed character other than one specifically given a magic meaning
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by 1003.2 (such magic meanings occur only in obsolete [``basic''] REs)
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is taken as an ordinary character.
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.PP
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Any unmatched [ is a REG_EBRACK error.
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.PP
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Equivalence classes cannot begin or end bracket-expression ranges.
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The endpoint of one range cannot begin another.
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.PP
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RE_DUP_MAX, the limit on repetition counts in bounded repetitions, is 255.
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.PP
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A repetition operator (?, *, +, or bounds) cannot follow another
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repetition operator.
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A repetition operator cannot begin an expression or subexpression
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or follow `^' or `|'.
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.PP
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`|' cannot appear first or last in a (sub)expression or after another `|',
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i.e. an operand of `|' cannot be an empty subexpression.
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An empty parenthesized subexpression, `()', is legal and matches an
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empty (sub)string.
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An empty string is not a legal RE.
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.PP
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A `{' followed by a digit is considered the beginning of bounds for a
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bounded repetition, which must then follow the syntax for bounds.
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A `{' \fInot\fR followed by a digit is considered an ordinary character.
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.PP
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`^' and `$' beginning and ending subexpressions in obsolete (``basic'')
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REs are anchors, not ordinary characters.
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.SH SEE ALSO
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.BR grep (1),
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.BR re_format (7).
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.PP
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POSIX 1003.2, sections 2.8 (Regular Expression Notation)
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and
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B.5 (C Binding for Regular Expression Matching).
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.SH DIAGNOSTICS
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Non-zero error codes from
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.B regcomp
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and
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.B regexec
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include the following:
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.PP
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.nf
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.ta \w'REG_ECOLLATE'u+3n
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REG_NOMATCH regexec() failed to match
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REG_BADPAT invalid regular expression
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REG_ECOLLATE invalid collating element
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REG_ECTYPE invalid character class
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REG_EESCAPE \e applied to unescapable character
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REG_ESUBREG invalid backreference number
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REG_EBRACK brackets [ ] not balanced
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REG_EPAREN parentheses ( ) not balanced
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REG_EBRACE braces { } not balanced
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REG_BADBR invalid repetition count(s) in { }
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REG_ERANGE invalid character range in [ ]
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REG_ESPACE ran out of memory
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REG_BADRPT ?, *, or + operand invalid
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REG_EMPTY empty (sub)expression
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REG_ASSERT ``can't happen''\(emyou found a bug
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REG_INVARG invalid argument, e.g. negative-length string
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.fi
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.SH HISTORY
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Originally written by Henry Spencer.
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Altered for inclusion in the 4.4BSD distribution.
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.SH BUGS
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This is an alpha release with known defects.
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|
Please report problems.
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.PP
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There is one known functionality bug.
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The implementation of internationalization is incomplete:
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the locale is always assumed to be the default one of 1003.2,
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and only the collating elements etc. of that locale are available.
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.PP
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The back-reference code is subtle and doubts linger about its correctness
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in complex cases.
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.PP
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.B Regexec
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performance is poor.
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This will improve with later releases.
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.I Nmatch
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exceeding 0 is expensive;
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.I nmatch
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exceeding 1 is worse.
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.B Regexec
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|
is largely insensitive to RE complexity \fIexcept\fR that back
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references are massively expensive.
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RE length does matter; in particular, there is a strong speed bonus
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for keeping RE length under about 30 characters,
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with most special characters counting roughly double.
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.PP
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.B Regcomp
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|
implements bounded repetitions by macro expansion,
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which is costly in time and space if counts are large
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or bounded repetitions are nested.
|
|
An RE like, say,
|
|
`((((a{1,100}){1,100}){1,100}){1,100}){1,100}'
|
|
will (eventually) run almost any existing machine out of swap space.
|
|
.PP
|
|
There are suspected problems with response to obscure error conditions.
|
|
Notably,
|
|
certain kinds of internal overflow,
|
|
produced only by truly enormous REs or by multiply nested bounded repetitions,
|
|
are probably not handled well.
|
|
.PP
|
|
Due to a mistake in 1003.2, things like `a)b' are legal REs because `)' is
|
|
a special character only in the presence of a previous unmatched `('.
|
|
This can't be fixed until the spec is fixed.
|
|
.PP
|
|
The standard's definition of back references is vague.
|
|
For example, does
|
|
`a\e(\e(b\e)*\e2\e)*d' match `abbbd'?
|
|
Until the standard is clarified,
|
|
behavior in such cases should not be relied on.
|
|
.PP
|
|
The implementation of word-boundary matching is a bit of a kludge,
|
|
and bugs may lurk in combinations of word-boundary matching and anchoring.
|