Hi monks,

I need to do a script which trims ends of strings if there is too many same letters at the end of the string. If there is 3 or more same letters in the end, I would like to shorten the string to have only two same letters. My initial version of doing this is below. 
#!/usr/bin/perl

use warnings;
use strict;

while (<DATA>) {
  chomp;
  print "$_ -> ";
  m/(\w)\Z/;
  my $last = $1;
  if (s/($last{3,})\Z/$last$last/) {
    my $len = length($1)-2;
    print "$len -> $_\n";
  } else { print "\n" }
}

__DATA__
ACTGCTAGGGGGGG
TCAGCTAGCNA
ACTGSCGACAAAA
GTCTGAGTTATTT

[download]
And the result of it is 
ACTGCTAGGGGGGG -> 5 -> ACTGCTAGG
TCAGCTAGCNA -> 
ACTGSCGACAAAA -> 2 -> ACTGSCGACAA
GTCTGAGTTATTT -> 1 -> GTCTGAGTTATT

[download]
The prints are there for sake of understanding the situation. However I do need the length of the trimmed string. Though I can of course just use length() after trimming to get it.

However I'm wondering if there is a better, or should I say faster, way of doing this. My inputs are several GB long and I would like to avoid a regex which needs to be recompiled at every time it is used (which it now does as there is a variable in the substitution). I thought of using the (??) construct but since I would need to "go back" after finding out the last character I couldn't come up with a workable solution.

In reply to Regex related question by Hena

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