Update: This node completely redone because several people posted before I did.

See perlfaq4

sub member {
           my $possible    = $_[0];
           my $array_ref   = $_[1];

           foreach my $member ( @{$array_ref} ) {
                   if ( $member eq $possible ) { return "1"; }
           }

           return "0";
   }
[download]

This is basically a glorified grep statement. But as the FAQ notes, that's inefficient. The trick is that you are looping over every element (until you hit it), EACH time you test. What you should do is contruct a hash of the values ONCE, and then you're good (as long as the list doesn't change).