my $script = param('select') or ...;
...
$dbh->do("UPDATE guestlog SET script='$script' WHERE host='$host'");

##</code><code>##

my $script = param('select') or ...;
...
$dbh->do("UPDATE guestlog SET script=? WHERE host=?", undef, $script, $host);

##</code><code>##

$sth = $dbh->prepare( "SELECT * FROM guestlog WHERE host='$host'");
$sth->execute();

##</code><code>##

$sth = $dbh->prepare("SELECT * FROM guestlog WHERE host=?");
$sth->execute($host);