# $action_string is set to something or other.

# actions is a hash whose keys are strings and whose values 
# are references to subroutines

my %actions = ( 
		'display'=> \&show_values(),
		'set'=>	\&set_values(),
		'default' => \&default()
		);

$action_string = 'default'  unless defined($action{$action_string});

$action{$action_string}->(); # calls the subroutine that this hash value is a reference to

sub set_values {
 # do something
}

sub show_values {
	# do something
}