Drat! Thanks for the reality check - the die was just there for testing, I should have taken it out as it does not add anything, similarly the for was a hold over from an earlier attempt. I've got to proof read my posts more!

You obviously have the same must-be-a-better-way (MBABW?) feeling, and I like the idea of the grep trick, though I must admit I usually have a fear of labels. Anyway your code will work with a few minor fixes:

my $s;
LIST:
for my $len ( 1..length $files[0]) {
  $s = substr($files[0],0,$len - 1);
  last LIST unless (scalar grep { /^$s/ } @files) == @files;
}
chop $s;
print "prefix: $s\n";
[download]

Update: Not silly at all bobn, I should really have specified that an empty string is the correct answer for no common prefix - thanks for pointing that out.

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I'd like to be able to assign to an luser