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 ``\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 ``&'' or ``\0'' or ``\
n'' or backslash. The use of backslashes in
subSpec tends to
interact badly with the Tcl parser's use of backslashes, so it's 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. 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 {\<foo\>} $string bar string
Insert double-quotes around the first instance of the word
interesting,
however it is capitalised.
regsub -nocase {\<interesting\>} $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 everything "bad"
set RE {[][{}\$\s\u0100-\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.
set quoted [subst [ regsub -all $RE $string $substitution]]
SEE ALSO¶
regexp(3tcl), re_syntax(3tcl), subst(3tcl)
KEYWORDS¶
match, pattern, regular expression, substitute