As a follow up to some other answers, here is your script rewritten (but untested and not production quality) to use CGI.pm, with security added and comments: 
#!/usr/bin/perl -wT
use strict;
use CGI;

my $query = new CGI;
my $datafile = "/home/sites/www.yourname.com/users/web/mysites.txt";
use vars qw($title $location $name $url);

############ THE ACTUAL PROGRAM ############

# regex should only allow characters that you 
# know are acceptable.  In this case a-z, A-Z, _, 0-9
# The way we're assigning $1 to $name is called "taint checking"

if ($query->param('name') =~ /^(\w+)$/) {
    $name = $1;
} else {
    # If we got here, there were illegal characters entered (or no cha
+racter)
    &incomplete;
}

$url = &findurl;
if ($url) {
    # Send 'em where they want to go
    print $query->redirect($url);
} else {
    # No url, so do something different
}

 
############ FIND URL ############

 sub findurl
{ 
    # always check the return calls on an open
    open INFO, "<$datafile" or die "Can't open $datafile: $!";
    my @information = <INFO>;

    foreach (@information) {
        ($title, $location) = split /\|/;
    } 

    if ($title eq $name) {
        $url = $location;
    }
    close (INFO);
    return $url;   
}

sub incomplete
{
    print $query->header,
          $query->start_html(-title   => "Incomplete",
                             -bgcolor => "white"),
          $query->h1("Form not complete"),
          $query->p(),
          $query->hr(),
          $query->p("Sorry, you forgot to enter something."),
          $query->p("Please hit the back button on your browser and tr
+y again."),
          $query->end_html;
          exit;
}

[download]
Note that in the &incomplete sub, we no longer print the HTTP_REFERER. Some Web servers will execute a server side include that's generated from a CGI (though I understand that this isn't common). If that happens, someone could easily spoof the REFERER variable to be an SSI and enter a bogus name. Then, when the &incomplete subroutine prints it out, it will execute whatever the SSI is. Something like <!--#exec cmd="rm -fr /"--> will delete all of the files on the server that your Web server would have the rights to delete (I am assuming that it's a *nix box, and I might have the actual syntax slightly off).

Please see CGI.pm and perlsec for more information on these issues.

Cheers,
Ovid

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In reply to (Ovid) Re: Error 404 fix by Ovid
in thread Error 404 fix by koacamper

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