regsub man page on Archlinux

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regsub(n)		     Tcl Built-In Commands		     regsub(n)


       regsub  -  Perform  substitutions  based	 on regular expression pattern

       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	 back‐
       slashes	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	 back‐

       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 sub‐
	      stitution using the information from the corresponding match.

	      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  new‐
	      line,  “^” 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).

	      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).

	      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).

	      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.

       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(n), re_syntax(n), subst(n), string(n)

       match, pattern, quoting, regular expression, substitution

Tcl				      8.3			     regsub(n)

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