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regexp.n
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'\"
'\" Copyright (c) 1993 The Regents of the University of California.
'\" All rights reserved.
'\"
'\" Permission is hereby granted, without written agreement and without
'\" license or royalty fees, to use, copy, modify, and distribute this
'\" documentation for any purpose, provided that the above copyright
'\" notice and the following two paragraphs appear in all copies.
'\"
'\" IN NO EVENT SHALL THE UNIVERSITY OF CALIFORNIA BE LIABLE TO ANY PARTY
'\" FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
'\" ARISING OUT OF THE USE OF THIS DOCUMENTATION, EVEN IF THE UNIVERSITY OF
'\" CALIFORNIA HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
'\"
'\" THE UNIVERSITY OF CALIFORNIA SPECIFICALLY DISCLAIMS ANY WARRANTIES,
'\" INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
'\" AND FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE PROVIDED HEREUNDER IS
'\" ON AN "AS IS" BASIS, AND THE UNIVERSITY OF CALIFORNIA HAS NO OBLIGATION TO
'\" PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
'\"
'\" $Header: /user6/ouster/tcl/man/RCS/regexp.n,v 1.2 93/06/17 13:31:37 ouster Exp $ SPRITE (Berkeley)
'\"
.so man.macros
.HS regexp tcl
.BS
'\" Note: do not modify the .SH NAME line immediately below!
.SH NAME
regexp \- Match a regular expression against a string
.SH SYNOPSIS
\fBregexp \fR?\fIswitches\fR? \fIexp string \fR?\fImatchVar\fR? ?\fIsubMatchVar subMatchVar ...\fR?
.BE
.SH DESCRIPTION
.PP
Determines whether the regular expression \fIexp\fR matches part or
all of \fIstring\fR and returns 1 if it does, 0 if it doesn't.
.LP
If additional arguments are specified after \fIstring\fR then they
are treated as the names of variables in which to return
information about which part(s) of \fIstring\fR matched \fIexp\fR.
\fIMatchVar\fR will be set to the range of \fIstring\fR that
matched all of \fIexp\fR. The first \fIsubMatchVar\fR will contain
the characters in \fIstring\fR that matched the leftmost parenthesized
subexpression within \fIexp\fR, the next \fIsubMatchVar\fR will
contain the characters that matched the next parenthesized
subexpression to the right in \fIexp\fR, and so on.
.LP
If the initial arguments to \fBregexp\fR start with \fB\-\fR then
.VS
they are treated as switches. The following switches are
currently supported:
.TP 10
\fB\-nocase\fR
Causes upper-case characters in \fIstring\fR to be treated as
lower case during the matching process.
.TP 10
\fB\-indices\fR
Changes what is stored in the \fIsubMatchVar\fRs.
Instead of storing the matching characters from \fBstring\fR,
each variable
will contain a list of two decimal strings giving the indices
in \fIstring\fR of the first and last characters in the matching
range of characters.
.TP 10
\fB\-\|\-\fR
Marks the end of switches. The argument following this one will
be treated as \fIexp\fR even if it starts with a \fB\-.
.VE
.LP
If there are more \fIsubMatchVar\fR's than parenthesized
subexpressions within \fIexp\fR, or if a particular subexpression
in \fIexp\fR doesn't match the string (e.g. because it was in a
portion of the expression that wasn't matched), then the corresponding
\fIsubMatchVar\fR will be set to ``\fB\-1 \-1\fR'' if \fB\-indices\fR
has been specified or to an empty string otherwise.
.SH "REGULAR EXPRESSIONS"
.PP
Regular expressions are implemented using Henry Spencer's package
(thanks, Henry!),
and the description of regular expressions below is copied verbatim
from his manual entry.
.PP
A regular expression is zero or more \fIbranches\fR, separated by ``|''.
It matches anything that matches one of the branches.
.PP
A branch is zero 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 ``*'', ``+'', or ``?''.
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 match of the atom, or the null string.
.PP
An atom is a regular expression in parentheses (matching a match for the
regular expression), a \fIrange\fR (see below), ``.''
(matching any single character), ``^'' (matching the null string at the
beginning of the input string), ``$'' (matching the null string at the
end of the input string), a ``\e'' followed by a single character (matching
that character), or a single character with no other significance
(matching that character).
.PP
A \fIrange\fR is a sequence of characters enclosed in ``[]''.
It normally matches any single character from the sequence.
If the sequence begins with ``^'',
it matches any single character \fInot\fR from the rest of the sequence.
If two characters in the sequence are separated by ``\-'', this is shorthand
for the full list of ASCII characters between them
(e.g. ``[0-9]'' matches any decimal digit).
To include a literal ``]'' in the sequence, make it the first character
(following a possible ``^'').
To include a literal ``\-'', make it the first or last character.
.PP
If a regular expression could match two different parts of a string,
it will match the one which begins earliest.
If both begin in the same place but match different lengths, or match
the same length in different ways, life gets messier, as follows.
.PP
In general, the possibilities in a list of branches are considered in
left-to-right order, the possibilities for ``*'', ``+'', and ``?'' are
considered longest-first, nested constructs are considered from the
outermost in, and concatenated constructs are considered leftmost-first.
The match that will be chosen is the one that uses the earliest
possibility in the first choice that has to be made.
If there is more than one choice, the next will be made in the same manner
(earliest possibility) subject to the decision on the first choice.
And so forth.
.PP
For example, ``(ab|a)b*c'' could match ``abc'' in one of two ways.
The first choice is between ``ab'' and ``a''; since ``ab'' is earlier, and does
lead to a successful overall match, it is chosen.
Since the ``b'' is already spoken for,
the ``b*'' must match its last possibility\(emthe empty string\(emsince
it must respect the earlier choice.
.PP
In the particular case where no ``|''s are present and there is only one
``*'', ``+'', or ``?'', the net effect is that the longest possible
match will be chosen.
So ``ab*'', presented with ``xabbbby'', will match ``abbbb''.
Note that if ``ab*'' is tried against ``xabyabbbz'', it
will match ``ab'' just after ``x'', due to the begins-earliest rule.
(In effect, the decision on where to start the match is the first choice
to be made, hence subsequent choices must respect it even if this leads them
to less-preferred alternatives.)
.SH KEYWORDS
match, regular expression, string