my @string 
  = sort { length $a <=> length $b }
  ( qw/ quux asdfasdfasdf asdfasdf asdfzxcv as / );
my $common = shift @string;
while ( my $teststr = shift @string and length $common ) {
    if ( $common eq substr( $teststr, 0, length $common ) ) {
        next;
    }
    my $flag = length $common;
    while ( $flag ) {
        if ( $common eq substr( $teststr, 0, $flag ) ) {
            $flag = 0;
        }
        else {
            $flag--;
            $common = substr( $common, 0, $flag );
        }
    }
}
# print $common;