- preg_replace: documentation ( source)
<?php
$text = 'My Name ## is #P_NAM3# and \r\n I am #P_AG2# years old';
$r = '#([^#]*)#';
//$r = '#(?P<name>.*?)#';
//$r = '#(\w*)#';
//preg_match_all('/'.$r.'/m', $text, $m);
//var_dump($m);
//$sustituciĆ³n = '${1}1,$3';
echo preg_replace('/'.$r.'/m', '$1_es', $text);