- substr: documentation ( source)
- rtrim: documentation ( source)
- strpos: documentation ( source)
- explode: documentation ( source)
<?php
$str = "achieve3000_Gestalt_students102713.txt";
$dat = substr($str, strpos("_", $str));
echo $dat;
list($prefix, $meat) = explode("_",$str, 2);
list($dat, $ext) = explode(".", $meat);
echo rtrim($dat, "0123456789");
?>