Well, it ain't off-the-shelf Perl. Maybe you mean something like:

use strict;
use warnings;

my $sitelist = xmlFileData ("Content", "Sitelist.txt");
my $Session;
my $str;

while (<$sitelist>) {
    chomp;
    next unless /\Q$Session->{'usrSystem'}\E/;
    $str .= MLX40Tutorials ();
}
[download]

However the code that you posted is so far from anything meaningful that it is pretty much impossible to decide just what you really want to happen.

I strongly recommend that you use strictures (use strict; use warnings;) which might at least make you focus a little on the scope of variables and where they get initialized.

Note that a straight character for character match is almost never what you want when processing XML. Perhaps you should tell us something about the bigger picture?