The following will trap some errors. Other problems could be related to your permissions, where you are outputting the stuff (/output.txt looks like it resides in the root directory, not in a directory writable by "nobody") at the beginning of the script do:

## Use the fabulous CGI.pm module is usually installed
use CGI;
my $C = CGI->new();

## create a code ref to the DIE event handler
$SIG{__DIE__} = \&my_die;

## create a sub to handle the dies

sub my_die {
    print $C->header,$C->start_html;
    print qq(<p>@_</p>);
    print $C->end_html;
}
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and let it go.

When you use the CGI module you can also pass parameters to the script from the command line that you would pass from the form. i.e.:

$ ./my_script.cgi username=tenatious password=hideyho! age=1000 IQ=1
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and lastly, make sure that the script is world executable:

chmod o+x my_script.cgi
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