Made xmlstarlet finding code hopefully more POSIX

http://mywiki.wooledge.org/BashFAQ/081

grep.php

@@ -1,10 +1,15 @@
 <?php
 header('Content-type: application/json');
 if (empty($_GET['q'])) { die(); }
+
+// Is this the correct way to sanitise args to shell from PHP?
 $QUERY=urldecode(escapeshellarg(urlencode($_GET['q'])));
+
+// Debug Logging
 //$fp = fopen('debug.log', 'a');
 //fwrite($fp, $_GET['q'] . " : " . $QUERY . "\n");
 //fclose($fp);
+
 exec("grep -hi $QUERY *.txt", $array);
 $data = json_encode($array);
 echo $_GET['jsoncallback'] . '(' . $data . ');';