use strict;
use warnings;

my $sampleData = <<DATA;
this and that
wibble
the other
DATA

open my $sitelist, '<', \$sampleData;
my $Session = {usrSystem => 'wibble'};
my $str;

while (<$sitelist>) {
    chomp;
    if (/\Q$Session->{'usrSystem'}\E/) {
        print "New stuff for $_\n";
    } else {
        print "Something else for $_\n";
    }
}

##</code><code>##

Something else for This and that
New stuff for wibble
Something else for the other