# create a string with binary data
my $binary="string\000with\000nulls";
# empty out the entry widget
$entrywidget->delete(0,"end");
# insert the data
$entrywidget->insert(0,$binary);
# pull back the data with get and compare to the
# original data
my $gotback=$entrywidget->get();

if ($binary ne $gotback) {
    print "hmm...buggy?\n";
    # throw in some hexdumps here ?
}