You could use a hash of coderefs:

my %actions = (
    ADD = \&add,
    DELETE = \&delete,
    REMOVE = \&remove,
);

# ...

if($action =~ /$monitoredActions/) {
    $_ = uc($action);
    if(exists $actions{$_}) {
        $actions{$_}->();
    } else {
        # undefined action. die/warn whatever
    }
}

sub add { ... }
sub delete { ... }
sub remove { ... }
[download]

Update: had misunderstood question.