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regsub(n) Tcl Built-In Commands regsub(n)
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NAME
regsub - Perform substitutions based on regular expression pattern matching
SYNOPSIS
regsub ?switches? exp string subSpec ?varName?
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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 sub-
Spec. If subSpec contains a "&" or "\0", then it is replaced in the substitution with the
portion of string that matched exp. If subSpec contains a "\n", 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 "&", "\0", "\n" and backslashes. The use
of backslashes in subSpec tends to interact badly with the Tcl parser's use of back-
slashes, so it is generally safest to enclose subSpec in braces if it includes back-
slashes.
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 "\n" 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 specifying 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 "$" matches an empty
string before any newline in addition to its normal function. This flag is
equivalent to specifying both -linestop and -lineanchor, or the (?n) embed-
ded option (see the re_syntax manual page).
-linestop Changes the behavior of "[^" bracket expressions and "." so that they stop
at newlines. This is the same as specifying the (?p) embedded option (see
the re_syntax manual page).
-lineanchor Changes the behavior of "^" and "$" (the "anchors") 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 interpreted in the same manner as the index |
argument to string index. When using this switch, "^" will not match the begin-
ning 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 man-
ual 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 "basic regular expression" syntax):
regsub -all {(?b)\<foo\>} $string bar string
Insert double-quotes around the first instance of the word interesting, however it is cap-
italized.
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 substitution {[format \\\\u%04x [scan "\\&" %c]]}
# Now we apply the substitution to get a subst-string that
# will perform 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, substitute
Tcl 8.3 regsub(n)
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