'\" te
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.\"  This notice shall appear on any product containing this material.
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.TH REGCOMP 3C "Nov 1, 2003"
.SH NAME
regcomp, regexec, regerror, regfree \- regular expression matching
.SH SYNOPSIS
.LP
.nf
#include <sys/types.h>
#include <regex.h>

\fBint\fR \fBregcomp\fR(\fBregex_t *restrict\fR \fIpreg\fR, \fBconst char *restrict\fR \fIpattern\fR,
     \fBint\fR \fIcflags\fR);
.fi

.LP
.nf
\fBint\fR \fBregexec\fR(\fBconst regex_t *restrict\fR \fIpreg\fR,
     \fBconst char *restrict\fR \fIstring\fR, \fBsize_t\fR \fInmatch\fR,
     \fBregmatch_t\fR \fIpmatch\fR[restrict], \fBint\fR \fIeflags\fR);
.fi

.LP
.nf
\fBsize_t\fR \fBregerror\fR(\fBint\fR \fIerrcode\fR, \fBconst regex_t *restrict\fR \fIpreg\fR,
     \fBchar *restrict\fR \fIerrbuf\fR, \fBsize_t\fR \fIerrbuf_size\fR);
.fi

.LP
.nf
\fBvoid\fR \fBregfree\fR(\fBregex_t *\fR\fIpreg\fR);
.fi

.SH DESCRIPTION
.sp
.LP
These functions interpret \fIbasic\fR and \fIextended\fR regular expressions
(described on the \fBregex\fR(5) manual page).
.sp
.LP
The structure type \fBregex_t\fR contains at least the following member:
.sp
.ne 2
.na
\fB\fBsize_t\fR \fBre_nsub\fR\fR
.ad
.RS 18n
Number of parenthesised subexpressions.
.RE

.sp
.LP
The structure type \fBregmatch_t\fR contains at least the following members:
.sp
.ne 2
.na
\fB\fBregoff_t\fR \fBrm_so\fR\fR
.ad
.RS 18n
Byte offset from start of \fIstring\fR to start of substring.
.RE

.sp
.ne 2
.na
\fB\fBregoff_t\fR \fBrm_eo\fR\fR
.ad
.RS 18n
Byte offset from start of \fIstring\fR of the first character after the end of
substring.
.RE

.SS "\fBregcomp()\fR"
.sp
.LP
The \fBregcomp()\fR function will compile the regular expression contained in
the string pointed to by the \fIpattern\fR argument and place the results in
the structure pointed to by \fIpreg\fR. The \fIcflags\fR argument is the
bitwise inclusive \fBOR\fR of zero or more of the following flags, which are
defined in the header \fB<regex.h>\fR:
.sp
.ne 2
.na
\fB\fBREG_EXTENDED\fR\fR
.ad
.RS 16n
Use Extended Regular Expressions.
.RE

.sp
.ne 2
.na
\fB\fBREG_ICASE\fR\fR
.ad
.RS 16n
Ignore case in match.
.RE

.sp
.ne 2
.na
\fB\fBREG_NOSUB\fR\fR
.ad
.RS 16n
Report only success/fail in \fBregexec()\fR.
.RE

.sp
.ne 2
.na
\fB\fBREG_NEWLINE\fR\fR
.ad
.RS 16n
Change the handling of \fBNEWLINE\fR characters, as described in the text.
.RE

.sp
.LP
The default regular expression type for \fIpattern\fR is a Basic Regular
Expression. The application can specify Extended Regular Expressions using the
\fBREG_EXTENDED\fR \fIcflags\fR flag.
.sp
.LP
If the \fBREG_NOSUB\fR flag was not set in \fIcflags\fR, then \fBregcomp()\fR
will set \fIre_nsub\fR to the number of parenthesised subexpressions (delimited
by \e(\e) in basic regular expressions or () in extended regular expressions)
found in \fI pattern\fR.
.SS "\fBregexec()\fR"
.sp
.LP
The \fBregexec()\fR function compares the null-terminated string specified by
\fIstring\fR with the compiled regular expression \fIpreg\fR initialized by a
previous call to \fBregcomp()\fR. The \fIeflags\fR argument is the bitwise
inclusive \fBOR\fR of zero or more of the following flags, which are defined in
the header <\fBregex.h\fR>:
.sp
.ne 2
.na
\fB\fBREG_NOTBOL\fR\fR
.ad
.RS 14n
The first character of the string pointed to by \fIstring\fR is not the
beginning of the line. Therefore, the circumflex character (\fI^\fR), when
taken as a special character, will not match the beginning of \fIstring\fR.
.RE

.sp
.ne 2
.na
\fB\fBREG_NOTEOL\fR\fR
.ad
.RS 14n
The last character of the string pointed to by \fIstring\fR is not the end of
the line. Therefore, the dollar sign (\fI$\fR), when taken as a special
character, will not match the end of \fIstring\fR.
.RE

.sp
.LP
If \fInmatch\fR is zero or \fBREG_NOSUB\fR was set in the \fIcflags\fR argument
to \fBregcomp()\fR, then \fBregexec()\fR will ignore the \fIpmatch\fR argument.
Otherwise, the \fIpmatch\fR argument must point to an array with at least
\fInmatch\fR elements, and \fBregexec()\fR will fill in the elements of that
array with offsets of the substrings of \fIstring\fR that correspond to the
parenthesised subexpressions of \fIpattern\fR:
\fIpmatch\fR\fB[\fR\fIi\fR\fB]\fR.\fIrm_so\fR will be the byte offset of the
beginning and \fIpmatch\fR\fB[\fR\fIi\fR\fB]\fR.\fIrm_eo\fR will be one greater
than the byte offset of the end of substring \fIi\fR. (Subexpression \fIi\fR
begins at the \fIi\fRth matched open parenthesis, counting from 1.) Offsets in
\fIpmatch\fR\fB[0]\fR identify the substring that corresponds to the entire
regular expression. Unused elements of \fIpmatch\fR up to
\fIpmatch\fR\fB[\fR\fInmatch\fR\fB\(mi1]\fR will be filled with \fB\(mi1\fR\&.
If there are more than \fInmatch\fR subexpressions in \fIpattern\fR
(\fIpattern\fR itself counts as a subexpression), then \fBregexec()\fR will
still do the match, but will record only the first \fInmatch\fR substrings.
.sp
.LP
When matching a basic or extended regular expression, any given parenthesised
subexpression of \fIpattern\fR might participate in the match of several
different substrings of \fIstring\fR, or it might not match any substring even
though the pattern as a whole did match. The following rules are used to
determine which substrings to report in \fIpmatch\fR when matching regular
expressions:
.sp
.ne 2
.na
\fB1.\fR
.ad
.RS 6n
If subexpression \fIi\fR in a regular expression is not contained within
another subexpression, and it participated in the match several times, then the
byte offsets in \fIpmatch\fR\fB[\fR\fIi\fR\fB]\fR will delimit the last such
match.
.RE

.sp
.ne 2
.na
\fB2.\fR
.ad
.RS 6n
If subexpression \fIi\fR is not contained within another subexpression, and it
did not participate in an otherwise successful match, the byte offsets in
\fIpmatch\fR\fB[\fR\fIi\fR\fB]\fR will be \fB\(mi1\fR\&. A subexpression does
not participate in the match when:
.sp
\fB*\fR or \fB\e{\e} \fR appears immediately after the subexpression in a basic
regular expression, or \fB*\fR, \fB?\fR, or \fB{\|}\fR appears immediately
after the subexpression in an extended regular expression, and the
subexpression did not match (matched zero times)
.sp
or
.sp
\fB|\fR is used in an extended regular expression to select this subexpression
or another, and the other subexpression matched.
.RE

.sp
.ne 2
.na
\fB3.\fR
.ad
.RS 6n
If subexpression \fIi\fR is contained within another subexpression \fIj\fR, and
\fIi\fR is not contained within any other subexpression that is contained
within \fIj\fR, and a match of subexpression \fIj\fR is reported in
\fIpmatch\fR\fB[\fR\fIj\fR\fB]\fR, then the match or non-match of subexpression
\fIi\fR reported in \fIpmatch\fR\fB[\fR\fIi\fR\fB]\fR will be as described in
1. and 2. above, but within the substring reported in
\fIpmatch\fR\fB[\fR\fIj\fR\fB]\fR rather than the whole string.
.RE

.sp
.ne 2
.na
\fB4.\fR
.ad
.RS 6n
If subexpression \fIi\fR is contained in subexpression \fIj\fR, and the byte
offsets in \fIpmatch\fR\fB[\fR\fIj\fR\fB]\fR are \fB\(mi1\fR, then the pointers
in \fIpmatch\fR\fB[\fR\fIi\fR\fB]\fR also will be \fB\(mi1\fR\&.
.RE

.sp
.ne 2
.na
\fB5.\fR
.ad
.RS 6n
If subexpression \fIi\fR matched a zero-length string, then both byte offsets
in \fIpmatch\fR\fB[\fR\fIi\fR\fB]\fR will be the byte offset of the character
or \fINULL\fR terminator immediately following the zero-length string.
.RE

.sp
.LP
If, when \fBregexec()\fR is called, the locale is different from when the
regular expression was compiled, the result is undefined.
.sp
.LP
If \fBREG_NEWLINE\fR is not set in \fIcflags\fR, then a \fBNEWLINE\fR character
in \fIpattern\fR or \fIstring\fR will be treated as an ordinary character. If
\fBREG_NEWLINE\fR is set, then newline will be treated as an ordinary character
except as follows:
.sp
.ne 2
.na
\fB1.\fR
.ad
.RS 6n
A \fBNEWLINE\fR character in \fIstring\fR will not be matched by a period
outside a bracket expression or by any form of a non-matching list.
.RE

.sp
.ne 2
.na
\fB2.\fR
.ad
.RS 6n
A circumflex (^) in \fIpattern\fR, when used to specify expression anchoring
will match the zero-length string immediately after a newline in \fIstring\fR,
regardless of the setting of \fBREG_NOTBOL\fR.
.RE

.sp
.ne 2
.na
\fB3.\fR
.ad
.RS 6n
A dollar-sign ($) in \fIpattern\fR, when used to specify expression anchoring,
will match the zero-length string immediately before a newline in \fIstring\fR,
regardless of the setting of \fBREG_NOTEOL.\fR
.RE

.SS "\fBregfree()\fR"
.sp
.LP
The \fBregfree()\fR function frees any memory allocated by \fBregcomp()\fR
associated with \fIpreg\fR.
.sp
.LP
The following constants are defined as error return values:
.sp
.ne 2
.na
\fB\fBREG_NOMATCH\fR\fR
.ad
.RS 16n
The \fBregexec()\fR function failed to match.
.RE

.sp
.ne 2
.na
\fB\fBREG_BADPAT\fR\fR
.ad
.RS 16n
Invalid regular expression.
.RE

.sp
.ne 2
.na
\fB\fBREG_ECOLLATE\fR\fR
.ad
.RS 16n
Invalid collating element referenced.
.RE

.sp
.ne 2
.na
\fB\fBREG_ECTYPE\fR\fR
.ad
.RS 16n
Invalid character class type referenced.
.RE

.sp
.ne 2
.na
\fB\fBREG_EESCAPE\fR\fR
.ad
.RS 16n
Trailing \e in pattern.
.RE

.sp
.ne 2
.na
\fB\fBREG_ESUBREG\fR\fR
.ad
.RS 16n
Number in \e\fIdigit\fR invalid or in error.
.RE

.sp
.ne 2
.na
\fB\fBREG_EBRACK\fR\fR
.ad
.RS 16n
\fB[\|]\fR imbalance.
.RE

.sp
.ne 2
.na
\fB\fBREG_ENOSYS\fR\fR
.ad
.RS 16n
The function is not supported.
.RE

.sp
.ne 2
.na
\fB\fBREG_EPAREN\fR\fR
.ad
.RS 16n
\fB\e(\|\e)\fR or \fB()\fR imbalance.
.RE

.sp
.ne 2
.na
\fB\fBREG_EBRACE\fR\fR
.ad
.RS 16n
\e{ \e} imbalance.
.RE

.sp
.ne 2
.na
\fB\fBREG_BADBR\fR\fR
.ad
.RS 16n
Content of \e{ \e} invalid: not a number, number too large, more than two
numbers, first larger than second.
.RE

.sp
.ne 2
.na
\fB\fBREG_ERANGE\fR\fR
.ad
.RS 16n
Invalid endpoint in range expression.
.RE

.sp
.ne 2
.na
\fB\fBREG_ESPACE\fR\fR
.ad
.RS 16n
Out of memory.
.RE

.sp
.ne 2
.na
\fB\fBREG_BADRPT\fR\fR
.ad
.RS 16n
?, * or + not preceded by valid regular expression.
.RE

.SS "\fBregerror()\fR"
.sp
.LP
The \fBregerror()\fR function provides a mapping from error codes returned by
\fBregcomp()\fR and \fBregexec()\fR to unspecified printable strings. It
generates a string corresponding to the value of the \fIerrcode\fR argument,
which must be the last non-zero value returned by \fBregcomp()\fR or
\fBregexec()\fR with the given value of \fIpreg\fR. If \fIerrcode\fR is not
such a value, an error message indicating that the error code is invalid is
returned.
.sp
.LP
If \fIpreg\fR is a \fINULL\fR pointer, but \fIerrcode\fR is a value returned by
a previous call to \fBregexec()\fR or \fBregcomp()\fR, the \fBregerror()\fR
still generates an error string corresponding to the value of \fIerrcode\fR.
.sp
.LP
If the \fIerrbuf_size\fR argument is not zero, \fBregerror()\fR will place the
generated string into the buffer of size \fIerrbuf_size\fR bytes pointed to by
\fIerrbuf\fR. If the string (including the terminating \fBNULL)\fR cannot fit
in the buffer, \fBregerror()\fR will truncate the string and null-terminate the
result.
.sp
.LP
If \fIerrbuf_size\fR is zero, \fBregerror()\fR ignores the \fIerrbuf\fR
argument, and returns the size of the buffer needed to hold the generated
string.
.sp
.LP
If the \fIpreg\fR argument to \fBregexec()\fR or \fBregfree()\fR is not a
compiled regular expression returned by \fBregcomp()\fR, the result is
undefined. A \fIpreg\fR is no longer treated as a compiled regular expression
after it is given to \fBregfree()\fR.
.sp
.LP
See \fBregex\fR(5) for BRE (Basic Regular Expression) Anchoring.
.SH RETURN VALUES
.sp
.LP
On successful completion, the \fBregcomp()\fR function returns \fB0\fR.
Otherwise, it returns an integer value indicating an error as described in
<\fBregex.h\fR>, and the content of \fIpreg\fR is undefined.
.sp
.LP
On successful completion, the \fBregexec()\fR function returns \fB0\fR.
Otherwise it returns \fBREG_NOMATCH\fR to indicate no match, or
\fBREG_ENOSYS\fR to indicate that the function is not supported.
.sp
.LP
Upon successful completion, the \fBregerror()\fR function returns the number of
bytes needed to hold the entire generated string. Otherwise, it returns \fB0\fR
to indicate that the function is not implemented.
.sp
.LP
The \fBregfree()\fR function returns no value.
.SH ERRORS
.sp
.LP
No errors are defined.
.SH USAGE
.sp
.LP
An application could use:
.sp
.LP
\fBregerror(code,preg,(char *)NULL,(size_t)0)\fR
.sp
.LP
to find out how big a buffer is needed for the generated string, \fBmalloc\fR a
buffer to hold the string, and then call \fBregerror()\fR again to get the
string (see \fBmalloc\fR(3C)). Alternately, it could allocate a fixed, static
buffer that is big enough to hold most strings, and then use \fBmalloc()\fR to
allocate a larger buffer if it finds that this is too small.
.SH EXAMPLES
.LP
\fBExample 1 \fRExample to match string against the extended regular expression
in pattern.
.sp
.in +2
.nf
#include <regex.h>
/*
* Match string against the extended regular expression in
* pattern, treating errors as no match.
*
* return 1 for match, 0 for no match
*/

int
match(const char *string, char *pattern)
{
      int status;
      regex_t re;
      if (regcomp(&re, pattern, REG_EXTENDED\||\|REG_NOSUB) != 0) {
           return(0);      /* report error */
      }
      status = regexec(&re, string, (size_t) 0, NULL, 0);
      regfree(&re);
      if (status != 0) {
            return(0);      /* report error */
      }
      return(1);
}
.fi
.in -2

.sp
.LP
The following demonstrates how the \fBREG_NOTBOL\fR flag could be used with
\fBregexec()\fR to find all substrings in a line that match a pattern supplied
by a user. (For simplicity of the example, very little error checking is done.)

.sp
.in +2
.nf
(void) regcomp (&re, pattern, 0);
/* this call to regexec(\|) finds the first match on the line */
error = regexec (&re, &buffer[0], 1, &pm, 0);
while (error == 0) {	/* while matches found */
        /* substring found between pm.rm_so and pm.rm_eo */
        /* This call to regexec(\|) finds the next match */
        error = regexec (&re, buffer + pm.rm_eo, 1, &pm, REG_NOTBOL);
}
.fi
.in -2

.SH ATTRIBUTES
.sp
.LP
See \fBattributes\fR(5) for descriptions of the following attributes:
.sp

.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
CSI	Enabled
_
Interface Stability	Standard
_
MT-Level	MT-Safe with exceptions
.TE

.SH SEE ALSO
.sp
.LP
\fBfnmatch\fR(3C), \fBglob\fR(3C), \fBmalloc\fR(3C), \fBsetlocale\fR(3C),
\fBattributes\fR(5), \fBstandards\fR(5), \fBregex\fR(5)
.SH NOTES
.sp
.LP
The \fBregcomp()\fR function can be used safely in a multithreaded application
as long as \fBsetlocale\fR(3C) is not being called to change the locale.