Do you have to write this to a file? It would make more sense to me to store it in a hash with the screen name, i.e.

my %sorry;
if ($msg=~/so?r?ry/){
  ++$sorry{"$screenname"};
}
[download]

but of course, you may need the file for something else, in which case I'd just store it in a hash anyway and replace the number in the file when you got a 'sry' in a message.