regsub - Perform substitutions based on regular expression pattern matching
regsub ?
switches?
exp string subSpec ?
varName?
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
“\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 backslashes, so it is generally safest to enclose
subSpec 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 “\
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 “$” matches an empty
string before any newline in addition to its normal function. This flag is
equivalent to specifying both -linestop and -lineanchor, or
the (?n) embedded option (see the re_syntax manual
page).
- -linestop
- Changes the behavior of “[^” bracket
expressions and “.” so that they stop at newlines. This is
the same as specifying the (?p) embedded option (see the
re_syntax manual page).
- -lineanchor
- Changes the behavior of “^” and
“$” (the “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 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.
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 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 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]]]
regexp(3tcl),
re_syntax(3tcl),
subst(3tcl),
string(3tcl)
match, pattern, quoting, regular expression, substitution