Actually, the print statement is probably much more expensive than any of those comparisons.

Anyway, I noodled with the script a bit.

#!/usr/bin/perl

use warnings;
use strict;

while ( <> ) {
    chomp;
    (/^\d{10}$/) ? print uniq($_)+0,"\n" : die "Not 10 digits.\n";
}

sub uniq { return $_[0] !~ /(.).*\1/ }
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