sub cmd_move {
    my ($package, $direction) = @_;
    print "You start to walk $direction, but suddenly remember that Grues live there\n";
}

while (<STDIN>) {
    chomp;
    my ($cmd, @args) = split(/\s+/, $_);
    $cmd = "cmd_$cmd";
    if (($cmd !~ /^\w+$/) || !main->can($cmd)) {
        print "Unknown command. Try again.\n";
    } else {
        main->$cmd(@args);
    }
}

##</code><code>##

package Commands;
sub cmd_move {....};
.
.
.
package main;
while (<STDIN>) {
  ...
  if (Commands->can($cmd)) {...}
}