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.\" Copyright (c) 1992, 1993, 1994 Henry Spencer.
.\" Copyright (c) 1992, 1993, 1994
.\" The Regents of the University of California. All rights reserved.
.\"
.\" This code is derived from software contributed to Berkeley by
.\" Henry Spencer.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\" must display the following acknowledgement:
.\" This product includes software developed by the University of
.\" California, Berkeley and its contributors.
.\" 4. Neither the name of the University nor the names of its contributors
.\" may be used to endorse or promote products derived from this software
.\" without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" @(#)regex.3 8.4 (Berkeley) 3/20/94
.\"
.TH REGEX 3 "7 October 1997" GNO "Library Routines"
.SH NAME
regcomp, regexec, regerror, regfree \- regular-expression library
.SH SYNOPSIS
#include <sys/types.h>
.br
#include <regex.h>
.HP
int \fBregcomp\fR(regex_t *\fIpreg\fR, const char *\fIpattern\fR,
int \fIcflags\fR);
.HP
int \fBregexec\fR(const regex_t *\fIpreg\fR, const char *\fIstring\fR,
size_t \fInmatch\fR, regmatch_t \fIpmatch\fR[], int \fIeflags\fR);
.HP
size_t \fBregerror\fR(int \fIerrcode\fR, const regex_t *\fIpreg\fR,
char *\fIerrbuf\fR, size_t \fIerrbuf_size\fR);
.HP
void \fBregfree\fR(regex_t *\fIpreg\fR);
.SH DESCRIPTION
These routines implement POSIX 1003.2 regular expressions (``RE''s);
see
.BR re_format (7).
.B regcomp
compiles an RE written as a string into an internal form,
.B regexec
matches that internal form against a string and reports results,
.B regerror
transforms error codes from either into human-readable messages,
and
.B regfree
frees any dynamically-allocated storage used by the internal form
of an RE.
.PP
The header
.B <regex.h>
declares two structure types,
.B regex_t
and
.BR regmatch_t ,
the former for compiled internal forms and the latter for match reporting.
It also declares the four functions,
a type
.BR regoff_t ,
and a number of constants with names starting with ``REG_''.
.PP
.B regcomp
compiles the regular expression contained in the
.I pattern
string,
subject to the flags in
.IR cflags ,
and places the results in the
.B 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
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.
.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
.BR regcomp .
.IP REG_ICASE
Compile for matching that ignores upper/lower case distinctions.
See
.BR re_format (7).
.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 `$' anchor matches the null string before any newline in the
string in addition to its normal function.
.IP REG_PEND
The regular expression ends,
not at the first NUL,
but just before the character pointed to by the
.B re_endp
member of the structure pointed to by
.IR preg .
The
.B re_endp
member is of type
.BR "const char *" .
This flag permits inclusion of NULs in the RE;
they are considered ordinary characters.
This is an extension,
compatible with but not specified by POSIX 1003.2,
and should be used with
caution in software intended to be portable to other systems.
.PP
When successful,
.B regcomp
returns 0 and fills in the structure pointed to by
.IR preg .
One member of that structure
(other than
.BR re_endp )
is publicized:
.BR re_nsub ,
of type
.BR size_t ,
contains the number of parenthesized subexpressions within the RE
(except that the value of this member is undefined if the
REG_NOSUB flag was used).
If
.B regcomp
fails, it returns a non-zero error code;
see DIAGNOSTICS.
.PP
.B Regexec
matches the compiled RE pointed to by
.B preg
against the
.IR string ,
subject to the flags in
.IR eflags ,
and reports results using
.IR nmatch ,
.IR pmatch ,
and the returned value.
The RE must have been compiled by a previous invocation of
.BR regcomp .
The compiled form is not altered during execution of
.BR regexec ,
so a single compiled RE can be used simultaneously by multiple threads.
.PP
By default,
the NUL-terminated string pointed to by
.I string
is considered to be the text of an entire line, minus any terminating
newline.
The
.I eflags
argument is the bitwise OR of zero or more of the following flags:
.IP REG_NOTBOL \w'REG_STARTEND'u+2n
The first character of
the string
is not the beginning of a line, so the `^' anchor should not match before it.
This does not affect the behavior of newlines under REG_NEWLINE.
.IP REG_NOTEOL
The NUL terminating
the string
does not end a line, so the `$' 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
.BR re_format (7)
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,
.B 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,
.B 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
.BR regmatch_t .
Such a structure has at least the members
.B rm_so
and
.BR rm_eo ,
both of type
.B regoff_t
(a signed arithmetic type at least as large as an
.B off_t
and a
.BR 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
.BR 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 ,
with subexpressions counted (starting at 1) by the order of their opening
parentheses in the RE, left to right.
Unused entries in the array\(emcorresponding either to subexpressions that
did not participate in the match at all, or to subexpressions that do not
exist in the RE (that is, \fIi\fR\ > \fIpreg\fR\->\fIre_nsub\fR)\(emhave both
.B rm_so
and
.B rm_eo
set to \-1.
If a subexpression participated in the match several times,
the reported substring is the last one it matched.
(Note, as an example in particular, that when the RE `(b*)+' matches `bbb',
the parenthesized subexpression matches each of the three `b's and then
an infinite number of empty strings following the last `b',
so the reported substring is one of the empties.)
.PP
If REG_STARTEND is specified,
.I pmatch
must point to at least one
.B regmatch_t
(even if
.I nmatch
is 0 or REG_NOSUB was specified),
to hold the input offsets for REG_STARTEND.
Use for output is still entirely controlled by
.IR nmatch ;
if
.I nmatch
is 0 or REG_NOSUB was specified,
the value of
.IR pmatch [0]
will not be changed by a successful
.IR regexec .
.PP
.B regerror
maps a non-zero
.I errcode
from either
.B regcomp
or
.B regexec
to a human-readable, printable message.
If
.I preg
is non-NULL,
the error code should have arisen from use of
the
.B regex_t
pointed to by
.IR preg ,
and if the error code came from
.BR regcomp ,
it should have been the result from the most recent
.B regcomp
using that
.IR regex_t .
.RB ( regerror
may be able to supply a more detailed message using information
from the
.BR regex_t .)
.B regerror
places the NUL-terminated message into the buffer pointed to by
.IR errbuf ,
limiting the length (including the NUL) to at most
.I errbuf_size
bytes.
If the whole message won't fit,
as much of it as will fit before the terminating NUL is supplied.
In any case,
the returned value is the size of buffer needed to hold the whole
message (including terminating NUL).
If
.I errbuf_size
is 0,
.I errbuf
is ignored but the return value is still correct.
.PP
If the
.I errcode
given to
.B regerror
is first ORed with REG_ITOA,
the ``message'' that results is the printable name of the error code,
e.g. ``REG_NOMATCH'',
rather than an explanation thereof.
If
.I errcode
is REG_ATOI,
then
.I preg
shall be non-NULL and the
.I re_endp
member of the structure it points to
must point to the printable name of an error code;
in this case, the result in
.I errbuf
is the decimal digits of
the numeric value of the error code
(0 if the name is not recognized).
REG_ITOA and REG_ATOI are intended primarily as debugging facilities;
they are extensions,
compatible with but not specified by POSIX 1003.2,
and should be used with
caution in software intended to be portable to other systems.
Be warned also that they are considered experimental and changes are possible.
.PP
.I Regfree
frees any dynamically-allocated storage associated with the compiled RE
pointed to by
.IR preg .
The remaining
.B regex_t
is no longer a valid compiled RE
and the effect of supplying it to
.B regexec
or
.B regerror
is undefined.
.PP
None of these functions references global variables except for tables
of constants;
all are safe for use from multiple threads if the arguments are safe.
.SH IMPLEMENTATION CHOICES
There are a number of decisions that 1003.2 leaves up to the implementor,
either by explicitly saying ``undefined'' or by virtue of them being
forbidden by the RE grammar.
This implementation treats them as follows.
.PP
See
.BR re_format (7)
for a discussion of the definition of case-independent matching.
.PP
There is no particular limit on the length of REs,
except insofar as memory is limited.
Memory usage is approximately linear in RE size, and largely insensitive
to RE complexity, except for bounded repetitions.
See BUGS for one short RE using them
that will run almost any system out of memory.
.PP
A backslashed character other than one specifically given a magic meaning
by 1003.2 (such magic meanings occur only in obsolete [``basic''] REs)
is taken as an ordinary character.
.PP
Any unmatched [ is a REG_EBRACK error.
.PP
Equivalence classes cannot begin or end bracket-expression ranges.
The endpoint of one range cannot begin another.
.PP
RE_DUP_MAX, the limit on repetition counts in bounded repetitions, is 255.
.PP
A repetition operator (?, *, +, or bounds) cannot follow another
repetition operator.
A repetition operator cannot begin an expression or subexpression
or follow `^' or `|'.
.PP
`|' cannot appear first or last in a (sub)expression or after another `|',
i.e. an operand of `|' cannot be an empty subexpression.
An empty parenthesized subexpression, `()', is legal and matches an
empty (sub)string.
An empty string is not a legal RE.
.PP
A `{' followed by a digit is considered the beginning of bounds for a
bounded repetition, which must then follow the syntax for bounds.
A `{' \fInot\fR followed by a digit is considered an ordinary character.
.PP
`^' and `$' beginning and ending subexpressions in obsolete (``basic'')
REs are anchors, not ordinary characters.
.SH SEE ALSO
grep(1), re_format(7)
.PP
POSIX 1003.2, sections 2.8 (Regular Expression Notation)
and
B.5 (C Binding for Regular Expression Matching).
.SH DIAGNOSTICS
Non-zero error codes from
.B regcomp
and
.B regexec
include the following:
.nf
REG_NOMATCH regexec() failed to match
REG_BADPAT invalid regular expression
REG_ECOLLATE invalid collating element
REG_ECTYPE invalid character class
REG_EESCAPE \e applied to unescapable character
REG_ESUBREG invalid backreference number
REG_EBRACK brackets [ ] not balanced
REG_EPAREN parentheses ( ) not balanced
REG_EBRACE braces { } not balanced
REG_BADBR invalid repetition count(s) in { }
REG_ERANGE invalid character range in [ ]
REG_ESPACE ran out of memory
REG_BADRPT ?, *, or + operand invalid
REG_EMPTY empty (sub)expression
REG_ASSERT ``can't happen''\(emyou found a bug
REG_INVARG invalid argument, e.g. negative-length string
.fi
.SH HISTORY
Originally written by Henry Spencer.
Altered for inclusion in the 4.4BSD distribution.
.SH BUGS
This is an alpha release with known defects.
Please report problems.
.PP
There is one known functionality bug.
The implementation of internationalization is incomplete:
the locale is always assumed to be the default one of 1003.2,
and only the collating elements etc. of that locale are available.
.PP
The back-reference code is subtle and doubts linger about its correctness
in complex cases.
.PP
.B regexec
performance is poor.
This will improve with later releases.
.I nmatch
exceeding 0 is expensive;
.I nmatch
exceeding 1 is worse.
.B regexec
is largely insensitive to RE complexity \fIexcept\fR that back
references are massively expensive.
RE length does matter; in particular, there is a strong speed bonus
for keeping RE length under about 30 characters,
with most special characters counting roughly double.
.PP
.B regcomp
implements bounded repetitions by macro expansion,
which is costly in time and space if counts are large
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.

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.\" Copyright (c) 1992, 1993, 1994 Henry Spencer.
.\" Copyright (c) 1992, 1993, 1994
.\" The Regents of the University of California. All rights reserved.
.\"
.\" This code is derived from software contributed to Berkeley by
.\" Henry Spencer.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\" must display the following acknowledgement:
.\" This product includes software developed by the University of
.\" California, Berkeley and its contributors.
.\" 4. Neither the name of the University nor the names of its contributors
.\" may be used to endorse or promote products derived from this software
.\" without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" @(#)re_format.7 8.3 (Berkeley) 3/20/94
.\"
.TH RE_FORMAT 7 "7 October 1997"
.SH NAME
re_format \- POSIX 1003.2 regular expressions
.SH DESCRIPTION
Regular expressions (``RE''s),
as defined in POSIX 1003.2, come in two forms:
modern REs (roughly those of
.BR egrep ;
1003.2 calls these ``extended'' REs)
and obsolete REs (roughly those of
.BR ed ;
1003.2 ``basic'' REs).
Obsolete REs mostly exist for backward compatibility in some old programs;
they will be discussed at the end.
1003.2 leaves some aspects of RE syntax and semantics open;
`\(dg' marks decisions on these aspects that
may not be fully portable to other 1003.2 implementations.
.PP
A (modern) RE is one\(dg or more non-empty\(dg \fIbranches\fR,
separated by `|'.
It matches anything that matches one of the branches.
.PP
A branch is one\(dg or more \fIpieces\fR, concatenated.
It matches a match for the first, followed by a match for the second, etc.
.PP
A piece is an \fIatom\fR possibly followed
by a single\(dg `*', `+', `?', or \fIbound\fR.
An atom followed by `*' matches a sequence of 0 or more matches of the atom.
An atom followed by `+' matches a sequence of 1 or more matches of the atom.
An atom followed by `?' matches a sequence of 0 or 1 matches of the atom.
.PP
A \fIbound\fR is `{' followed by an unsigned decimal integer,
possibly followed by `,'
possibly followed by another unsigned decimal integer,
always followed by `}'.
The integers must lie between 0 and RE_DUP_MAX (255\(dg) inclusive,
and if there are two of them, the first may not exceed the second.
An atom followed by a bound containing one integer \fIi\fR
and no comma matches
a sequence of exactly \fIi\fR matches of the atom.
An atom followed by a bound
containing one integer \fIi\fR and a comma matches
a sequence of \fIi\fR or more matches of the atom.
An atom followed by a bound
containing two integers \fIi\fR and \fIj\fR matches
a sequence of \fIi\fR through \fIj\fR (inclusive) matches of the atom.
.PP
An atom is a regular expression enclosed in `()' (matching a match for the
regular expression),
an empty set of `()' (matching the null string)\(dg,
a \fIbracket expression\fR (see below), `.'
(matching any single character), `^' (matching the null string at the
beginning of a line), `$' (matching the null string at the
end of a line), a `\e' followed by one of the characters
`^.[$()|*+?{\e'
(matching that character taken as an ordinary character),
a `\e' followed by any other character\(dg
(matching that character taken as an ordinary character,
as if the `\e' had not been present\(dg),
or a single character with no other significance (matching that character).
A `{' followed by a character other than a digit is an ordinary
character, not the beginning of a bound\(dg.
It is illegal to end an RE with `\e'.
.PP
A \fIbracket expression\fR is a list of characters enclosed in `[]'.
It normally matches any single character from the list (but see below).
If the list begins with `^',
it matches any single character
(but see below) \fInot\fR from the rest of the list.
If two characters in the list are separated by `\-', this is shorthand
for the full \fIrange\fR of characters between those two (inclusive) in the
collating sequence,
e.g. `[0-9]' in ASCII matches any decimal digit.
It is illegal\(dg for two ranges to share an
endpoint, e.g. `a-c-e'.
Ranges are very collating-sequence-dependent,
and portable programs should avoid relying on them.
.PP
To include a literal `]' in the list, make it the first character
(following a possible `^').
To include a literal `\-', make it the first or last character,
or the second endpoint of a range.
To use a literal `\-' as the first endpoint of a range,
enclose it in `[.' and `.]' to make it a collating element (see below).
With the exception of these and some combinations using `[' (see next
paragraphs), all other special characters, including `\e', lose their
special significance within a bracket expression.
.PP
Within a bracket expression, a collating element (a character,
a multi-character sequence that collates as if it were a single character,
or a collating-sequence name for either)
enclosed in `[.' and `.]' stands for the
sequence of characters of that collating element.
The sequence is a single element of the bracket expression's list.
A bracket expression containing a multi-character collating element
can thus match more than one character,
e.g. if the collating sequence includes a `ch' collating element,
then the RE `[[.ch.]]*c' matches the first five characters
of `chchcc'.
.PP
Within a bracket expression, a collating element enclosed in `[=' and
`=]' is an equivalence class, standing for the sequences of characters
of all collating elements equivalent to that one, including itself.
(If there are no other equivalent collating elements,
the treatment is as if the enclosing delimiters were `[.' and `.]'.)
For example, if o and \o'o^' are the members of an equivalence class,
then `[[=o=]]', `[[=\o'o^'=]]', and `[o\o'o^']' are all synonymous.
An equivalence class may not\(dg be an endpoint
of a range.
.PP
Within a bracket expression, the name of a \fIcharacter class\fR enclosed
in `[:' and `:]' stands for the list of all characters belonging to that
class.
Standard character class names are:
.PP
.RS
.nf
alnum digit punct
alpha graph space
blank lower upper
cntrl print xdigit
.fi
.RE
.PP
These stand for the character classes defined in
.IR ctype (3).
A locale may provide others.
A character class may not be used as an endpoint of a range.
.PP
There are two special cases\(dg of bracket expressions:
the bracket expressions `[[:<:]]' and `[[:>:]]' match the null string at
the beginning and end of a word respectively.
A word is defined as a sequence of
word characters
which is neither preceded nor followed by
word characters.
A word character is an
.I alnum
character (as defined by
.IR ctype (3))
or an underscore.
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
In the event that an RE could match more than one substring of a given
string,
the RE matches the one starting earliest in the string.
If the RE could match more than one substring starting at that point,
it matches the longest.
Subexpressions also match the longest possible substrings, subject to
the constraint that the whole match be as long as possible,
with subexpressions starting earlier in the RE taking priority over
ones starting later.
Note that higher-level subexpressions thus take priority over
their lower-level component subexpressions.
.PP
Match lengths are measured in characters, not collating elements.
A null string is considered longer than no match at all.
For example,
`bb*' matches the three middle characters of `abbbc',
`(wee|week)(knights|nights)' matches all ten characters of `weeknights',
when `(.*).*' is matched against `abc' the parenthesized subexpression
matches all three characters, and
when `(a*)*' is matched against `bc' both the whole RE and the parenthesized
subexpression match the null string.
.PP
If case-independent matching is specified,
the effect is much as if all case distinctions had vanished from the
alphabet.
When an alphabetic that exists in multiple cases appears as an
ordinary character outside a bracket expression, it is effectively
transformed into a bracket expression containing both cases,
e.g. `x' becomes `[xX]'.
When it appears inside a bracket expression, all case counterparts
of it are added to the bracket expression, so that (e.g.) `[x]'
becomes `[xX]' and `[^x]' becomes `[^xX]'.
.PP
No particular limit is imposed on the length of REs\(dg.
Programs intended to be portable should not employ REs longer
than 256 bytes,
as an implementation can refuse to accept such REs and remain
POSIX-compliant.
.PP
Obsolete (``basic'') regular expressions differ in several respects.
`|', `+', and `?' are ordinary characters and there is no equivalent
for their functionality.
The delimiters for bounds are `\e{' and `\e}',
with `{' and `}' by themselves ordinary characters.
The parentheses for nested subexpressions are `\e(' and `\e)',
with `(' and `)' by themselves ordinary characters.
`^' is an ordinary character except at the beginning of the
RE or\(dg the beginning of a parenthesized subexpression,
`$' is an ordinary character except at the end of the
RE or\(dg the end of a parenthesized subexpression,
and `*' is an ordinary character if it appears at the beginning of the
RE or the beginning of a parenthesized subexpression
(after a possible leading `^').
Finally, there is one new type of atom, a \fIback reference\fR:
`\e' followed by a non-zero decimal digit \fId\fR
matches the same sequence of characters
matched by the \fId\fRth parenthesized subexpression
(numbering subexpressions by the positions of their opening parentheses,
left to right),
so that (e.g.) `\e([bc]\e)\e1' matches `bb' or `cc' but not `bc'.
.SH SEE ALSO
.BR regex (3)
.PP
POSIX 1003.2, section 2.8 (Regular Expression Notation).
.SH BUGS
Having two kinds of REs is a botch.
.PP
The current 1003.2 spec says that `)' is an ordinary character in
the absence of an unmatched `(';
this was an unintentional result of a wording error,
and change is likely.
Avoid relying on it.
.PP
Back references are a dreadful botch,
posing major problems for efficient implementations.
They are also somewhat vaguely defined
(does
`a\e(\e(b\e)*\e2\e)*d' match `abbbd'?).
Avoid using them.
.PP
1003.2's specification of case-independent matching is vague.
The ``one case implies all cases'' definition given above
is current consensus among implementors as to the right interpretation.
.PP
The syntax for word boundaries is incredibly ugly.

7
usr.man/mkso.data
View File

@ -1,7 +1,7 @@
# 0
# 1 The first column is the "real" man page; the second is the .so link.
# 2
# 3 $Id: mkso.data,v 1.5 1997/10/03 05:46:31 gdr Exp $
# 3 $Id: mkso.data,v 1.6 1997/10/08 07:09:08 gdr Exp $
# 4
man2/alarm.2 man2/alarm10.2
man2/chdir.2 man2/fchdir.2
@ -201,6 +201,10 @@ man3/queue.3 man3/TAILQ_INSERT_BEFORE.3
man3/queue.3 man3/TAILQ_INSERT_HEAD.3
man3/queue.3 man3/TAILQ_INSERT_TAIL.3
man3/queue.3 man3/TAILQ_REMOVE.3
man3/regex.3 man3/regcomp.3
man3/regex.3 man3/regexec.3
man3/regex.3 man3/regerror.3
man3/regex.3 man3/regfree.3
man3/scanf.3 man3/fscanf.3
man3/scanf.3 man3/sscanf.3
man3/scanf.3 man3/vfscanf.3
@ -241,3 +245,4 @@ man3/tmpnam.3 man3/tmpfile.3
man3/ttyname.3 man3/isatty.3
man3/ttyname.3 man3/ttyslot.3
man5/utmp.5 man5/wtmp.5
man7/re.format.7 man7/re_format.7