Basically I was wondering if I could use s/ to call a function that would manipulate one of the matches and use that as the replacement string.
This is code that sort of represents what I am trying to explain. 
my $foo = 'bar 123 moo cow';

$foo = s/(123)/function($1)/;

sub function
 {
   my $argument = shift;
   $argument = "rab";
   return $argument;
 }

[download]
The basic idea is that 123 is replaced by what function returns. Obviously the operation it represents could be easily done via s/ but this is just the example instead of what I am actually trying to do with &function

In reply to using s/ to not only substitute but also modify text by Anonymous Monk

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