See winregex.html for a description of regular expressions and why this port was originally done, which was to support the use of regular expressions from C programs such as SIOD in the WIN32 environment.
However, because system-supplied regular expression support is still generally missing from some Unix environments, and also from VMS, it has proven to be more convenient to bundle the hs_regex package with siod itself. Yes, you'll find nearly the same code in the Apache web server, and perhaps a dozen other places.
The following source files are utilized and are covered by the copyright noted at the end of this document:
cclass.h regcomp.c regex2.h regfree.c cname.h regerror.c utils.h engine.c regex.h regexec.c
Preformatted manual-style pages:
NAME
regcomp, regexec, regerror, regfree - regular-expression
library
SYNOPSIS
#include <sys/types.h>
#include <regex.h>
int regcomp(regex_t *preg, const char *pattern, int cflags);
int regexec(const regex_t *preg, const char *string,
size_t nmatch, regmatch_t pmatch[], int eflags);
size_t regerror(int errcode, const regex_t *preg,
char *errbuf, size_t errbuf_size);
void regfree(regex_t *preg);
DESCRIPTION
These routines implement POSIX 1003.2 regular expressions
(``RE''s); see re_format(7). Regcomp compiles an RE written
as a string into an internal form, regexec matches that
internal form against a string and reports results, regerror
transforms error codes from either into human-readable mes-
sages, and regfree frees any dynamically-allocated storage
used by the internal form of an RE.
The header <regex.h> declares two structure types, regex_t
and regmatch_t, the former for compiled internal forms and
the latter for match reporting. It also declares the four
functions, a type regoff_t, and a number of constants with
names starting with ``REG_''.
Regcomp compiles the regular expression contained in the
pattern string, subject to the flags in cflags, and places
the results in the regex_t structure pointed to by preg.
Cflags is the bitwise OR of zero or more of the following
flags:
REG_EXTENDED Compile modern (``extended'') REs, rather than
the obsolete (``basic'') REs that are the
default.
REG_BASIC This is a synonym for 0, provided as a coun-
terpart to REG_EXTENDED to improve readabil-
ity.
REG_NOSPEC Compile with recognition of all special char-
acters turned off. All characters are thus
considered ordinary, so the ``RE'' is a
literal string. This is an extension, compa-
tible 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 regcomp.
REG_ICASE Compile for matching that ignores upper/lower
case distinctions. See re_format(7).
REG_NOSUB Compile for matching that need only report
success or failure, not what was matched.
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 new-
line 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.
REG_PEND The regular expression ends, not at the first
NUL, but just before the character pointed to
by the re_endp member of the structure pointed
to by preg. The re_endp member is of type
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.
When successful, regcomp returns 0 and fills in the struc-
ture pointed to by preg. One member of that structure
(other than re_endp) is publicized: re_nsub, of type
size_t, contains the number of parenthesized subexpressions
within the RE (except that the value of this member is unde-
fined if the REG_NOSUB flag was used). If regcomp fails, it
returns a non-zero error code; see DIAGNOSTICS.
Regexec matches the compiled RE pointed to by preg against
the string, subject to the flags in eflags, and reports
results using nmatch, pmatch, and the returned value. The
RE must have been compiled by a previous invocation of
regcomp. The compiled form is not altered during execution
of regexec, so a single compiled RE can be used simultane-
ously by multiple threads.
By default, the NUL-terminated string pointed to by string
is considered to be the text of an entire line, minus any
terminating newline. The eflags argument is the bitwise OR
NAME
re_format - POSIX 1003.2 regular expressions
DESCRIPTION
Regular expressions (``RE''s), as defined in POSIX 1003.2,
come in two forms: modern REs (roughly those of egrep;
1003.2 calls these ``extended'' REs) and obsolete REs
(roughly those of ed; 1003.2 ``basic'' REs). Obsolete REs
mostly exist for backward compatibility in some old pro-
grams; they will be discussed at the end. 1003.2 leaves
some aspects of RE syntax and semantics open; ` - ' marks
decisions on these aspects that may not be fully portable to
other 1003.2 implementations.
A (modern) RE is one- or more non-empty- branches, separated
by `|'. It matches anything that matches one of the
branches.
A branch is one- or more pieces, concatenated. It matches a
match for the first, followed by a match for the second,
etc.
A piece is an atom possibly followed by a single- `*', `+',
`?', or bound. 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.
A bound is `{' followed by an unsigned decimal integer, pos-
sibly followed by `,' possibly followed by another unsigned
decimal integer, always followed by `}'. The integers must
lie between 0 and RE_DUP_MAX (255-) inclusive, and if there
are two of them, the first may not exceed the second. An
atom followed by a bound containing one integer i and no
comma matches a sequence of exactly i matches of the atom.
An atom followed by a bound containing one integer i and a
comma matches a sequence of i or more matches of the atom.
An atom followed by a bound containing two integers i and j
matches a sequence of i through j (inclusive) matches of the
atom.
An atom is a regular expression enclosed in `()' (matching a
match for the regular expression), an empty set of `()'
(matching the null string) - , a bracket expression (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 `\' followed by one
of the characters `^.[$()|*+?{\' (matching that character
taken as an ordinary character), a `\' followed by any other
character- (matching that character taken as an ordinary
character, as if the `\' had not been present-), or a single
character with no other significance (matching that charac-
ter). A `{' followed by a character other than a digit is
an ordinary character, not the beginning of a bound-. It is
illegal to end an RE with `\'.
A bracket expression 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) not from the
rest of the list. If two characters in the list are
separated by ` -', this is shorthand for the full range of
characters between those two (inclusive) in the collating
sequence, e.g. `[0-9]' in ASCII matches any decimal digit.
It is illegal- 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.
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 end-
point of a range. To use a literal `-' as the first end-
point 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 `\', lose their special
significance within a bracket expression.
Within a bracket expression, a collating element (a charac-
ter, 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 charac-
ters of that collating element. The sequence is a single
element of the bracket expression's list. A bracket expres-
sion 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'.
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 ^ are the members of an equivalence class, then
`[[=o=]]', `[[=^=]]', and `[o^]' are all synonymous. An
equivalence class may not- be an endpoint of a range.
Within a bracket expression, the name of a character class
enclosed in `[:' and `:]' stands for the list of all charac-
ters belonging to that class. Standard character class
names are:
alnum digit punct
alpha graph space
blank lower upper
cntrl print xdigit
These stand for the character classes defined in ctype(3).
A locale may provide others. A character class may not be
used as an endpoint of a range.
There are two special cases- 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 alnum character (as defined by ctype(3)) or
an underscore. This is an extension, compatible with but
not specified by POSIX 1003.2, and should be used with cau-
tion in software intended to be portable to other systems.
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 sub-
string 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.
Match lengths are measured in characters, not collating ele-
ments. 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.
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 expres-
sion, it is effectively transformed into a bracket expres-
sion containing both cases, e.g. `x' becomes `[xX]'. When
it appears inside a bracket expression, all case counter-
parts of it are added to the bracket expression, so that
(e.g.) `[x]' becomes `[xX]' and `[^x]' becomes `[^xX]'.
No particular limit is imposed on the length of REs-. Pro-
grams 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.
Obsolete (``basic'') regular expressions differ in several
respects. `|', `+', and `?' are ordinary characters and
there is no equivalent for their functionality. The delim-
iters for bounds are `\{' and `\}', with `{' and `}' by
themselves ordinary characters. The parentheses for nested
subexpressions are `\(' and `\)', with `(' and `)' by them-
selves ordinary characters. `^' is an ordinary character
except at the beginning of the RE or- the beginning of a
parenthesized subexpression, `$' is an ordinary character
except at the end of the RE or- 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 back reference:
`\' followed by a non-zero decimal digit d matches the same
sequence of characters matched by the dth parenthesized
subexpression (numbering subexpressions by the positions of
their opening parentheses, left to right), so that (e.g.)
`\([bc]\)\1' matches `bb' or `cc' but not `bc'.
SEE ALSO
regex(3)
POSIX 1003.2, section 2.8 (Regular Expression Notation).
BUGS
Having two kinds of REs is a botch.
The current 1003.2 spec says that `)' is an ordinary charac-
ter in the absence of an unmatched `('; this was an uninten-
tional result of a wording error, and change is likely.
Avoid relying on it.
Back references are a dreadful botch, posing major problems
for efficient implementations. They are also somewhat
vaguely defined (does `a\(\(b\)*\2\)*d' match `abbbd'?).
Avoid using them.
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.
The syntax for word boundaries is incredibly ugly.
Copyright 1992, 1993, 1994 Henry Spencer. All rights reserved. This software is not subject to any license of the American Telephone and Telegraph Company or of the Regents of the University of California. Permission is granted to anyone to use this software for any purpose on any computer system, and to alter it and redistribute it, subject to the following restrictions: 1. The author is not responsible for the consequences of use of this software, no matter how awful, even if they arise from flaws in it. 2. The origin of this software must not be misrepresented, either by explicit claim or by omission. Since few users ever read sources, credits must appear in the documentation. 3. Altered versions must be plainly marked as such, and must not be misrepresented as being the original software. Since few users ever read sources, credits must appear in the documentation. 4. This notice may not be removed or altered. =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= /*- * Copyright (c) 1994 * The Regents of the University of California. All rights reserved. * * 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. * * @(#)COPYRIGHT 8.1 (Berkeley) 3/16/94 */