for my $key (keys %opts) {
         print $key, " ", dhcp_option($key),"\t";
         if (ref($opts{$key}) =~ m/ARRAY/) {
             print $_, " " foreach (@{$opts{$key}});
         }
         # NOTE: elsif can just be else, as a string
         # necessarily does or does not match /ARRAY/
         elsif (ref($opts{$key}) !~ /ARRAY/) {
             print $opts{$key};
         }
         print "\n";
     }

     # OR (untested):
 
     for my $key (keys %opts) {
         print "$key ", dhcp_option($key), "\t",
               ( ref($opts{$key}) =~ /ARRAY/  
                    ? join" ", @{$opts{$key}} 
                    : $opts{$key}
               )
               "\n";
     }