#! perl -slw
use strict;

sub random_string {
    my $n    = shift;
    my $result = '';

    my @letters   = ('A'..'Z', 'a'..'z');
    my @letternum = ('A'..'Z', 'a'..'z', '0'..'9');

    $result .= $letters[ rand $#letters ];
    $result .= join "", map { $letternum[ rand $#letternum ] } 1..$n;

    return $result;
}
my %h;

printf("\r$_"), $h{ random_string( $ARGV[0] ) }++ and die "Dup after $_ reps" for 1 .. 1e6;