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 subSpec.  If subSpec contains a "&" or "", then it is replaced in the substitution with the portion of  string  that
       matched	exp.   If subSpec 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  inter-
       pretation of "&", "", "
" 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 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 sub-
		 stitution 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 "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.

EXAMPLES

       Replace (in the string in variable string) every instance of foo which is a word by itself with bar:
	      regsub -all {mfooM} $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 {yinterestingy} $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 {[][{};#\$ 
	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 {
 {\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)