use vars qw(%Config); # "global" ist dafuer manchmal besser

my $cgi = CGI->new();
my $action = $cgi->param('action') || 'default';

%Config = (
  default => { subroutine => \&Default, ... },
  action1 => { subroutine => \&Action1, ... },
  action2 => { subroutine => \&Action2, ... },
);

if (exists $Config{$action} and exists $Config{$action}->{subroutine}) {
  $Config{$action}->{subroutine}->($cgi, ...);
}
else { # call default, or errorhandling, or whatever
  $Config{default}->{subroutine}->($cgi, ...);
} # else