use CGI;

my $cgih = CGI->new;

my $par1 = $cgih->param('par1');
my $par2 = $cgih->param('par2');

my $formular = qq(
<FORM>
<INPUT TYPE="CHECKBOX" NAME="par1" VALUE="true"> Parameter 1
<INPUT TYPE="CHECKBOX" NAME="par2" VALUE="true"> Parameter 2
<INPUT TYPE="BUTTON" NAME="senden" VALUE="aktualisieren">
</FORM>
);

if ($cgih->param('senden')) {
  # verarbeite Parameter
}
else { # sonst Formular ausgeben
  print $cgih->header, $formular;
}