Gets the first key-value pair from the named map
in the named domain.
The NIS domain name.
The NIS map.
Returns the first key-value pair as an array on success, or FALSE on
$entry = yp_first($domain, "passwd.byname");
$key = key($entry);
$value = $entry[$key];
echo "First entry in this map has key " . $key . " and value " . $value;