use Template;
my $TMPL = Template->new();
my $res;
$TMPL->process( \*DATA, {
                          screen => qw(screen1 screen2)[rand 2]
                        }, \$res );
print "$res\n";
__END__
[% INCLUDE "$screen" %]

[% BLOCK screen1 %]
This is screen #1.
[% END %]

[% BLOCK screen2 %]
This is screen #2.
[% END %]