- substr: documentation ( source)
- var_dump: documentation ( source)
- preg_replace_callback: documentation ( source)
<?php
$torrent = 'd8:announce37:http://blender.waag.org:6969/announce13:creation datei1212070099e4:infod6:lengthi196898674e4:name30:big_buck_bunny_720p_stereo.ogg12:piece lengthi262144e6:pieces15040:DñÀsÑ45/';
$regex = "/(lengthi[0-9]+e)/i";
$sizes = array();
preg_replace_callback($regex, function($matches) use(&$sizes)
{
$sizes[] = substr($matches[2], 0, $matches[1]);
}, $torrent);
var_dump($sizes); // I want to get "262144", you can see this just before "pieces", top right