# in init phase:
my $commands = join "|", keys %myhash;
my $command_regex = qr/^($commands)\s*(.*)$/i;

# in input loop:
while(<STDIN>)
{
   if ( m/$command_regex/o )
   {
      my $command = lc $1;
      $myhash{ $command }->( $2 );
   } else {
      $myhash{"error"}->( $_ );
   }
}