Assuming you have a hash ('%usernames') of the usernames already taken: 
my $username;
foreach (@usernames) {
    if (!exists $usernames{$_}) {
        $username = $_;
        last;
    }
}

[download]
After which, '$username' will either contain the first unused username from '@usernames', or be undefined, if none were available.

In reply to Re: can I get a loop? by kilinrax
in thread can I get a loop? by Anonymous Monk

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