#!/usr/bin/perl -w

use CGI;
use strict;
my $page = CGI::new();
my $input = $page->param('checkbox1');
if ($input eq 'on') {
    # do something
} else {
    # do something else
}
exit (0);
[download]

Checkboxes don't have values unless you give them one. If they are checked, the name=value pair is sent. Otherwise, IIRC, nothing is sent. So in your HTML, you need:

<input type="checkbox" name="blort" value="foo">
[download]

In other words, your form will work if your HTML is exactly like this:

<input type="checkbox" name="checkbox1" value="on">
[download]

Then value=pair in this case would be checkbox1=on (if checked obviously). I disagree that if not checked your $input{'checkbox1'} would be undefined. That would vary depdending on the query string parsing method. It may be null, but not necessarily undef. This might be a source for errors down the road.

If the checkbox is not checked then it will not get posted to the query string. There will be no reference what-so-ever to the paramater (checkbox1 in this case). So the exists function mention below would probably be the easiest.

Maybe this is just with my server (Apache), but I dont think so.

However, just setting a value of on in the html and then checking for that value in the script should always work. Whether undefined or null, it definately won't equal the string "on" so...

if (defined ($cb_value = $input{checkbox1}) {
    # do something
} else {
    # do something less exciting
}
[download]

if(exists $input{'checkbox1'}) {
[download]