#!/usr/bin/php
<?php

$xml = file_get_contents('php://stdin');

$pattern = '/([0-9]*)<\/per-minute>\s*<\/metronome>\s*<\/direction-type>.*?<\/staff>/ims';
$replacement = '$0'."\n".'    <sound tempo="$1"/>';

echo preg_replace($pattern, $replacement, $xml);

?>