regex.3

regex-spencer-3.8-src.zip

.TH REGEX 3 "25 Sept 1997"
.BY "Henry Spencer"
.de ZR
.\" one other place knows this name:  the SEE ALSO section
.IR regex (7) \\$1
..
.SH NAME
regcomp, regexec, regerror, regfree \- regular-expression library
.SH SYNOPSIS
.ft B
.\".na
#include <sys/types.h>
.br
#include <regex.h>
.HP 10
int regcomp(regex_t\ *preg, const\ char\ *pattern, int\ cflags);
.HP
int\ regexec(const\ regex_t\ *preg, const\ char\ *string,
size_t\ nmatch, regmatch_t\ pmatch[], int\ eflags);
.HP
size_t\ regerror(int\ errcode, const\ regex_t\ *preg,
char\ *errbuf, size_t\ errbuf_size);
.HP
void\ regfree(regex_t\ *preg);
.\".ad
.ft
.SH DESCRIPTION
These routines implement POSIX 1003.2 regular expressions (``RE''s);
see
.ZR .
.I Regcomp
compiles an RE written as a string into an internal form,
.I regexec
matches that internal form against a string and reports results,
.I regerror
transforms error codes from either into human-readable messages,
and
.I regfree
frees any dynamically-allocated storage used by the internal form
of an RE.
.PP
The header
.I <regex.h>
declares two structure types,
.I regex_t
and
.IR regmatch_t ,
the former for compiled internal forms and the latter for match reporting.
It also declares the four functions,
a type
.IR regoff_t ,
and a number of constants with names starting with ``REG_''.
.PP
.I Regcomp
compiles the regular expression contained in the
.I pattern
string,
subject to the flags in
.IR cflags ,
and places the results in the
.I regex_t
structure pointed to by
.IR preg .
.I Cflags
is the bitwise OR of zero or more of the following flags:
.IP REG_EXTENDED \w'REG_EXTENDED'u+2n
Compile modern (``extended'') REs,
rather than the obsolete (``basic'') REs that
are the default.
.IP REG_BASIC
This is a synonym for 0,
provided as a counterpart to REG_EXTENDED to improve readability.
This is an extension,
compatible with but not specified by POSIX 1003.2,
and should be used with
caution in software intended to be portable to other systems.
.IP REG_NOSPEC
Compile with recognition of all special characters turned off.
All characters are thus considered ordinary,
so the ``RE'' is a literal string.
This is an extension,
compatible with but not specified by POSIX 1003.2,
and should be used with
caution in software intended to be portable to other systems.
REG_EXTENDED and REG_NOSPEC may not be used
in the same call to
.IR regcomp .
.IP REG_ICASE
Compile for matching that ignores upper/lower case distinctions.
See
.ZR .
.IP REG_NOSUB
Compile for matching that need only report success or failure,
not what was matched.
.IP REG_NEWLINE
Compile for newline-sensitive matching.
By default, newline is a completely ordinary character with no special
meaning in either REs or strings.
With this flag,
`[^' bracket expressions and `.' never match newline,
a `^' anchor matches the null string after any newline in the string
in addition to its normal function,
and the `$' anchor matches the null string before any newline in the
string in addition to its normal function.
.IP REG_PEND
The regular expression ends,
not at the first NUL,
but just before the character pointed to by the
.I re_endp
member of the structure pointed to by
.IR preg .
The
.I re_endp
member is of type
.IR const\ char\ * .
This flag permits inclusion of NULs in the RE;
they are considered ordinary characters.
This is an extension,
compatible with but not specified by POSIX 1003.2,
and should be used with
caution in software intended to be portable to other systems.
.PP
When successful,
.I regcomp
returns 0 and fills in the structure pointed to by
.IR preg .
One member of that structure
(other than
.IR re_endp )
is publicized:
.IR re_nsub ,
of type
.IR size_t ,
contains the number of parenthesized subexpressions within the RE
(except that the value of this member is undefined if the
REG_NOSUB flag was used).
If
.I regcomp
fails, it returns a non-zero error code;
see DIAGNOSTICS.
.PP
.I Regexec
matches the compiled RE pointed to by
.I preg
against the
.IR string ,
subject to the flags in
.IR eflags ,
and reports results using
.IR nmatch ,
.IR pmatch ,
and the returned value.
The RE must have been compiled by a previous invocation of
.IR regcomp .
The compiled form is not altered during execution of
.IR regexec ,
so a single compiled RE can be used simultaneously by multiple threads.
.PP
By default,
the NUL-terminated string pointed to by
.I string
is considered to be the text of an entire line,
with the NUL indicating the end of the line.
(That is,
any other end-of-line marker is considered to have been removed
and replaced by the NUL.)
The
.I eflags
argument is the bitwise OR of zero or more of the following flags:
.IP REG_NOTBOL \w'REG_STARTEND'u+2n
The first character of
the string
is not the beginning of a line, so the `^' anchor should not match before it.
This does not affect the behavior of newlines under REG_NEWLINE.
.IP REG_NOTEOL
The NUL terminating
the string
does not end a line, so the `$' anchor should not match before it.
This does not affect the behavior of newlines under REG_NEWLINE.
.IP REG_STARTEND
The string is considered to start at
\fIstring\fR\ + \fIpmatch\fR[0].\fIrm_so\fR
and to have a terminating NUL located at
\fIstring\fR\ + \fIpmatch\fR[0].\fIrm_eo\fR
(there need not actually be a NUL at that location),
regardless of the value of
.IR nmatch .
See below for the definition of
.IR pmatch
and
.IR nmatch .
This is an extension,
compatible with but not specified by POSIX 1003.2,
and should be used with
caution in software intended to be portable to other systems.
Note that a non-zero \fIrm_so\fR does not imply REG_NOTBOL;
REG_STARTEND affects only the location of the string,
not how it is matched.
.PP
See
.ZR
for a discussion of what is matched in situations where an RE or a
portion thereof could match any of several substrings of
.IR string .
.PP
Normally,
.I regexec
returns 0 for success and the non-zero code REG_NOMATCH for failure.
Other non-zero error codes may be returned in exceptional situations;
see DIAGNOSTICS.
.PP
If REG_NOSUB was specified in the compilation of the RE,
or if
.I nmatch
is 0,
.I regexec
ignores the
.I pmatch
argument (but see below for the case where REG_STARTEND is specified).
Otherwise,
.I pmatch
points to an array of
.I nmatch
structures of type
.IR regmatch_t .
Such a structure has at least the members
.I rm_so
and
.IR rm_eo ,
both of type
.I regoff_t
(a signed arithmetic type at least as large as an
.I off_t
and a
.IR ssize_t ),
containing respectively the offset of the first character of a substring
and the offset of the first character after the end of the substring.
Offsets are measured from the beginning of the
.I string
argument given to
.IR regexec .
An empty substring is denoted by equal offsets,
both indicating the character following the empty substring.
.PP
The 0th member of the
.I pmatch
array is filled in to indicate what substring of
.I string
was matched by the entire RE.
Remaining members report what substring was matched by parenthesized
subexpressions within the RE;
member
.I i
reports subexpression
.IR i ,