Php

Error Log

 cat /var/log/apache2/error.log

Arrays

 array_key_exists(key,array);

JSON

 json_decode($str, true);
 json_encode($obj);

The true makes it associative.

Files

 readfile($filename);

Ouputs the file to stdOut.

 file_put_contents($filename, $str);

Write string to file.