'\"
'\" Copyright (c) 1993 The Regents of the University of California.
'\" Copyright (c) 1994-1996 Sun Microsystems, Inc.
'\" Copyright (c) 2000 Scriptics Corporation.
'\"
'\" See the file "license.terms" for information on usage and redistribution
'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
'\" 
'\" RCS: @(#) $Id: regsub.n,v 1.1.1.1 2005/03/01 06:51:54 chenyu Exp $
'\" 
.so man.macros
.TH regsub n 8.3 Tcl "Tcl Built-In Commands"
.BS
'\" Note:  do not modify the .SH NAME line immediately below!
.SH NAME
regsub \- Perform substitutions based on regular expression pattern matching
.SH SYNOPSIS
\fBregsub \fR?\fIswitches\fR? \fIexp string subSpec varName\fR
.BE

.SH DESCRIPTION
.PP
This command matches the regular expression \fIexp\fR against
\fIstring\fR,
and it copies \fIstring\fR to the variable whose name is
given by \fIvarName\fR.
(Regular expression matching is described in the \fBre_syntax\fR
reference page.)
If there is a match, then while copying \fIstring\fR to \fIvarName\fR
the portion of \fIstring\fR that
matched \fIexp\fR is replaced with \fIsubSpec\fR.
If \fIsubSpec\fR contains a ``&'' or ``\e0'', then it is replaced
in the substitution with the portion of \fIstring\fR that
matched \fIexp\fR.
If \fIsubSpec\fR contains a ``\e\fIn\fR'', where \fIn\fR is a digit
between 1 and 9, then it is replaced in the substitution with
the portion of \fIstring\fR that matched the \fIn\fR-th
parenthesized subexpression of \fIexp\fR.
Additional backslashes may be used in \fIsubSpec\fR to prevent special
interpretation of ``&'' or ``\e0'' or ``\e\fIn\fR'' or
backslash.
The use of backslashes in \fIsubSpec\fR tends to interact badly
with the Tcl parser's use of backslashes, so it's generally
safest to enclose \fIsubSpec\fR in braces if it includes
backslashes.
.LP
If the initial arguments to \fBregexp\fR start with \fB\-\fR then
they are treated as switches.  The following switches are
currently supported:
.TP 10
\fB\-all\fR
All ranges in \fIstring\fR that match \fIexp\fR are found and
substitution is performed for each of these ranges.
Without this switch only the first
matching range is found and substituted.
If \fB\-all\fR is specified, then ``&'' and ``\e\fIn\fR''
sequences are handled for each substitution using the information
from the corresponding match.
.TP 15
\fB\-expanded\fR
Enables use of the expanded regular expression syntax where
whitespace and comments are ignored.  This is the same as specifying
the \fB(?x)\fR embedded option (see METASYNTAX, below).
.TP 15
\fB\-line\fR
Enables newline-sensitive matching.  By default, newline is a
completely ordinary character with no special meaning.  With this
flag, `[^' bracket expressions and `.' never match newline, `^'
matches an empty string after any newline in addition to its normal
function, and `$' matches an empty string before any newline in
addition to its normal function.  This flag is equivalent to
specifying both \fB\-linestop\fR and \fB\-lineanchor\fR, or the
\fB(?n)\fR embedded option (see METASYNTAX, below).
.TP 15
\fB\-linestop\fR
Changes the behavior of `[^' bracket expressions and `.' so that they
stop at newlines.  This is the same as specifying the \fB(?p)\fR
embedded option (see METASYNTAX, below).
.TP 15
\fB\-lineanchor\fR
Changes the behavior of `^' and `$' (the ``anchors'') so they match the
beginning and end of a line respectively.  This is the same as
specifying the \fB(?w)\fR embedded option (see METASYNTAX, below).
.TP 10
\fB\-nocase\fR
Upper-case characters in \fIstring\fR will be converted to lower-case
before matching against \fIexp\fR;  however, substitutions specified
by \fIsubSpec\fR use the original unconverted form of \fIstring\fR.
.VS 8.3
.TP 10
\fB\-start\fR \fIindex\fR
Specifies a character index offset into the string to start
matching the regular expression at.  When using this switch, `^'
will not match the beginning of the line, and \\A will still
match the start of the string at \fIindex\fR.
\fIindex\fR will be constrained to the bounds of the input string.
.VE 8.3
.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\-\fR.
.PP
The command returns a count of the number of matching ranges that
were found and replaced.
See the manual entry for \fBregexp\fR for details on the interpretation
of regular expressions.

.SH KEYWORDS
match, pattern, regular expression, substitute

