Perl binary search function

Recently I need to implement a binary searching with perl, so I got this code:

 use strict;
 use warnings;
 
 my $want = shift;
 die "$0 number" unless defined $want;
 
 my @list= (3,5,7,11,13,17,19);

 my $pos=bin_search(\@list,$want);
 print "Position: ", defined $pos ? $pos : "undef","\n";

 # binary search
 sub bin_search {
     my $array = shift;
     my $find  = shift;
 
     my ($l,$r)=(0,$#$array);
 
     while ($l<=$r) {
         my $m=int(($l+$r)/2);
 
         if ($find<$array->[$m]) {
             $r=$m-1;
         } elsif ($find>$array->[$m]) {
             $l=$m+1;
         } else {
             return $m;
         }
     }
     return undef;
 } 

It’s smart. Run it this way:

$ perl binarysearch.pl 11
 Position: 3
$ perl binarysearch.pl 13
 Position: 4
$ perl binarysearch.pl 15
 Position: undef 

It’s much faster than loop through the entire array to match the element.