my @usernames = qw(zero one two three four five six);
testswap(\@usernames);
print join(" ", @usernames), "\n";

sub testswap {
 my $array = shift;
 my $i = 2;
 my $j = 5;
 @$array[$i, $j] = @$array[$j, $i];
}

##</code><code>##

zero one five three four two six

##</code><code>##

my $username = $usernames[rand(@usernames)];