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Sparse and Greedy matching - Tcl 8.4

Problem Analysis Once you have done a sparse or greedy count, all your following counts will also be sparse or greedy - this is a well documented bug in Tcl 8.4!

tcl courseReminder ...
.* is a greedy match - any character and AS MANY AS POSSIBLE
.*? is a sparse match - any character but AS FEW AS POSSIBLE

set demo abc@def@ghi@jkl
#
# Correctly working greedy matches
regexp (.*)@(.*) $demo all first second
puts "$first and $second"
#
# Correctly working sparse matches
regexp (.*?)@(.*?) $demo all first second
puts "$first and $second"
#
# Both matches will be SPARSE here
regexp (.*?)@(.*) $demo all first second
puts "$first and $second"
#
# Both matches will be GREEDY here
regexp (.*)@(.*?) $demo all first second
puts "$first and $second"


Running that, we get:

earth-wind-and-fire:~/oct07/camb grahamellis$ tclsh spag
abc@def@ghi and jkl
abc and
abc and
abc@def@ghi and jkl
earth-wind-and-fire:~/oct07/camb grahamellis$


Suggested Work-around

You can emulate a sparse match by excluding the delimiter character from he group that you would be sparse matching, and using a greedy match.

Thus
regexp (.*?)@(.*) $demo all first second
can be rewritten as
regexp {([^@]*)@(.*)} $demo all first second
if you really needed sparse followed by greedy!

result:
abc and def@ghi@jkl

(written 2007-10-27, updated 2011-03-01)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
T247 - Tcl/Tk - Advanced Regular Expressions
  [4205] Regular Expression Substitution - Tcl - (2013-11-12)
  [1613] Regular expression for 6 digits OR 25 digits - (2008-04-16)
  [1410] Tcl / regsub - changing a string and using interesting bits - (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)
  [943] Matching within multiline strings, and ignoring case in regular expressions - (2006-11-25)


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