[php] Best way to get hostname with php

For PHP >= 5.3.0 use this:

$hostname = gethostname();

For PHP < 5.3.0 but >= 4.2.0 use this:

$hostname = php_uname('n');

For PHP < 4.2.0 use this:

$hostname = getenv('HOSTNAME'); 
if(!$hostname) $hostname = trim(`hostname`); 
if(!$hostname) $hostname = exec('echo $HOSTNAME');
if(!$hostname) $hostname = preg_replace('#^\w+\s+(\w+).*$#', '$1', exec('uname -a'));