regsub(n) Tcl Built-In Commands regsub(n)
NAME
regsub - Perform substitutions based on regular expression pattern
matching
SYNOPSIS
regsub ?switches? exp string subSpec ?varName?
DESCRIPTION
This command matches the regular expression exp against string, and
either copies string to the variable whose name is given by varName or
returns string if varName is not present. (Regular expression matching
is described in the re_syntax reference page.) If there is a match,
then while copying string to varName (or to the result of this command
if varName is not present) the portion of string that matched exp is
replaced with subSpec. If subSpec contains a or then it is replaced in
the substitution with the portion of string that matched exp. If sub-
Spec contains a where n is a digit between 1 and 9, then it is replaced
in the substitution with the portion of string that matched the n'th
parenthesized subexpression of exp. Additional backslashes may be used
in subSpec to prevent special interpretation of and backslashes. The
use of backslashes in subSpec tends to interact badly with the Tcl
parser's use of backslashes, so it is generally safest to enclose sub-
Spec in braces if it includes backslashes.
If the initial arguments to regsub start with - then they are treated
as switches. The following switches are currently supported:
-all All ranges in string that match exp are found and substitution
is performed for each of these ranges. Without this switch only
the first matching range is found and substituted. If -all is
specified, then and sequences are handled for each substitution
using the information from the corresponding match.
-expanded
Enables use of the expanded regular expression syntax where
whitespace and comments are ignored. This is the same as speci-
fying the (?x) embedded option (see the re_syntax manual page).
-line 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 -linestop and -lineanchor, or the (?n) embedded
option (see the re_syntax manual page).
-linestop
Changes the behavior of bracket expressions and so that they
stop at newlines. This is the same as specifying the (?p)
embedded option (see the re_syntax manual page).
-lineanchor
Changes the behavior of and (the so they match the beginning and
end of a line respectively. This is the same as specifying the
(?w) embedded option (see the re_syntax manual page).
-nocase
Upper-case characters in string will be converted to lower-case
before matching against exp; however, substitutions specified
by subSpec use the original unconverted form of string.
-start index
Specifies a character index offset into the string to start
matching the regular expression at. The index value is inter-
preted in the same manner as the index argument to string index.
When using this switch, will not match the beginning of the
line, and \A will still match the start of the string at index.
index will be constrained to the bounds of the input string.
-- Marks the end of switches. The argument following this one will
be treated as exp even if it starts with a -.
If varName is supplied, the command returns a count of the number of
matching ranges that were found and replaced, otherwise the string
after replacement is returned. See the manual entry for regexp for
details on the interpretation of regular expressions.
EXAMPLES
Replace (in the string in variable string) every instance of foo which
is a word by itself with bar:
regsub -all {\mfoo\M} $string bar string
or (using the syntax):
regsub -all {(?b)\<foo\>} $string bar string
Insert double-quotes around the first instance of the word interesting,
however it is capitalized.
regsub -nocase {\yinteresting\y} $string {"&"} string
Convert all non-ASCII and Tcl-significant characters into \u escape
sequences by using regsub and subst in combination:
# This RE is just a character class for almost everything "bad" set RE
{[][{};#\\\$ \r\t\u0080-\uffff]}
# We will substitute with a fragment of Tcl script in brackets set sub-
stitution {[format \\\\u%04x [scan "\\&" %c]]}
# Now we apply the substitution to get a subst-string that # will per-
form the computational parts of the conversion. Note # that newline is
handled specially through string map since # backslash-newline is a
special sequence. set quoted [subst [string map {\n {\\u000a}} \
[regsub -all $RE $string $substitution]]]
SEE ALSO
regexp(n), re_syntax(n), subst(n), string(n)
KEYWORDS
match, pattern, quoting, regular expression, substitution
Tcl 8.3 regsub(n)
tcl 8.6.0 - Generated Fri Jan 11 14:39:01 CST 2013