$re = '/\s-\s\d*.\d*\sMB/';
$str = '<a href="http://example.com/a0j8nm5l3wo0" target=_blank>01 song name.mp3 - 2.4 MB</a>
<a href="http://example.com/ic1jfhhzzfth" target=_blank>02 song name.mp3 - 4.0 MB</a>
<a href="http://example.com/zo2nv6bzy6gd" target=_blank>03 song name.mp3 - 3.3 MB</a>
<a href="http://example.com/5fyony1m4j0w" target=_blank>04 song name.mp3 - 3.5 MB</a>
<a href="http://example.com/3imswet27clg" target=_blank>05 song name.mp3 - 1.9 MB</a>
<a href="http://example.com/ml65j3gpdggv" target=_blank>06 song name.mp3 - 3.4 MB</a>
<a href="http://example.com/hmuk8il0a04j" target=_blank>07 song name.mp3 - 4.4 MB</a>
<a href="http://example.com/qx81e67ystd3" target=_blank>08 song name.mp3 - 3.9 MB</a>
<a href="http://example.com/g6fo1s64vzkj" target=_blank>09 song name.mp3 - 3.9 MB</a>
<a href="http://example.com/xo3hw4xyx372" target=_blank>10 song name.mp3 - 3.6 MB</a>
<a href="http://example.com/ivcth22eqygd" target=_blank>11 song name.mp3 - 3.3 MB</a>';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php