Something that's relatively simple is to have a hash, with the keys being the command, and the values being anonymous subroutines.

 my %command=
  (
     shutdown    => sub { print "Shutting down...\n"; exit 0; },
     lock_user   => sub { my ($user) = @_;
                      # Insert code to lock $user here.
                    },
     unlock_user => sub { my ($user) = @_;
                      # Insert code here to unlock $user
                    },
     show        => sub {  # Insert show code here
                    },
     lock        => sub {
                        $_ = shift;
                        if ($command{lock_$_}) {
                           $command{lock_$_}->(@_);
                        } else {
                           die "Don't know how to lock $_\n";
                        }
                    },
     unlock      => sub {
                        $_ = shift;
                        if ($command{unlock_$_}) {
                           $command{unlock_$_}->(@_);
                        } else {
                           die "Don't know how to unlock $_\n";
                        }
                    },
      help        => sub {# update per L~R's suggestion:
                         print "Current commands: ";
                         print join "\n", sort {
                         $a cmp $b } keys %command;
                    },
   );

  my ($cmd, @args) = @ARGV; # Or however you get them.
  $cmd = lc $cmd; # Force lowercase per L~R's suggestion.
  my $sub = $command{$cmd};
  $sub = $command{help} if not defined $sub;
  $sub->(@args);
[download]

$;=sub{$/};@;=map{my($a,$b)=($_,$;);$;=sub{$a.$b->()}}
split//,".rekcah lreP rehtona tsuJ";$\=$ ;->();print$/
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