Let's take it from the top:

my $mech = WWW::Mechanize->new();
my $stream = HTML::TokeParser->new(\$html);
my $streamm = HTML::TokeParser->new(\$htmll);
my $streammm = HTML::TokeParser->new(\$htmlll);
my %dep;
my %dep2;
my @coursename;
$mech->get($url);
$html = $mech->content();
[download]

You need to declare $html, $htmll, etc. prior to initializing $stream, $streamm, etc.
Fix that first, and update the code.

Please use strict; It would have caught undeclared variables.

Also heed the advice at: How do I post a question effectively?