Before you get assaulted by the CGI.pm police (Update: too late! :-), here's what you should really be doing up front:

#!/usr/local/bin/perl -wT

use strict;
use CGI;

my $q = CGI->new();

print $q->header();

# Using CGI is even easier than doing it yourself,
# so PLEASE(!) use it!
$studentid = $q->param('studentid');
$CSC = $q->param('CSC');
chomp($CSC);  
$assignment = $q->param('assignment');
$file = $q->param('file');
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Now, consider constructing a path from variables, such as you are trying to do. Instead of using string interpolation, such as "$HOME/$x/$y", you should just join:

my $path = join ('/',
                   $HOME, 'classes', $CSC,
                   $studentid, $assignment,
                   'outputfile.txt');
[download]

Of course, before you even think of doing this, you must validate your parameters to make sure they are "kosher". Using 'perl' with the '-T' parameter makes user data tainted, or icky, and your program will fail with errors unless you check them out first.

# An example of "validated" input
my ($studentid) = $q->param('studentid') =~ /(\w+)/;
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You should define your input specification as narrow as possible. For example, if you just wanted numbers, you can use '\d+'. If none of this makes any sense, a quick browse through the regular expressions reference will help immensely. This is time well spent.

You should note that CGI.pm helped you by:

• Not having to write your own "text/html" header.
• Not having to test for various methods (POST vs. GET)
• Not having to worry about de-mangling %-ified parameters
• Not having to handle more than one instance of the same parameter name (i.e. a "CHECKBOX" with one-or-more selections possible)

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