Tcl / regsub - changing a string and using interesting bits

Regexp matches a string to a regular expression, and regsub goes one further in that it replaces the found string with something else, saving the transformed output into a new variable. But what if I want the output pattern to include part of the string that was matched? I can refer to the "interesting bits" using \1, \2, etc, if I wish.

Example:

# In Tcl, 

#       regub needle haystack newneedle saveithere

#

# Refer to matches in the newneedle via \1

# Example - to surround dogs, cats and rabbits with !s

#

regsub -all (cat|dog|rabbit) "The cat and dog and budgie" \

  {!\1!} result

puts $result

Results:

earth-wind-and-fire:~/oct07/camb grahamellis$ tclsh rsd

The !cat! and !dog! and budgie

earth-wind-and-fire:~/oct07/camb grahamellis$

(written 2007-10-27, updated 2007-10-30)

Associated topics are indexed under

T205 - Tcl/Tk - String Handling in Tcl
  [3576] Tcl - apparently odd behaviour of string trimleft - (2012-01-13)
  [3285] Extracting data from a string / line from file - Tcl - (2011-05-10)
  [3192] Tcl - Some example of HOW TO in handling data files and formats - (2011-03-04)
  [2472] split and join in tcl and expect - (2009-10-23)
  [1601] Replacing the last comma with an and - (2008-04-04)
  [1403] Square Bracket protection in Tcl - (2007-10-23)
  [943] Matching within multiline strings, and ignoring case in regular expressions - (2006-11-25)
  [779] The fragility of pancakes - and better structures - (2006-06-26)
  [404] How to check that a string contains a number in Tcl - (2005-08-06)

T247 - Tcl/Tk - Advanced Regular Expressions
  [1613] Regular expression for 6 digits OR 25 digits - (2008-04-16)
  [1412] Sparse and Greedy matching - Tcl 8.4 - (2007-10-27)
  [1336] Ignore case in Regular Expression - (2007-09-08)
  [1305] Regular expressions made easy - building from components - (2007-08-16)
  [1195] Regular Express Primer - (2007-05-20)

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