<?php
// list of keys to ignore (including the name of this variable)
$ignore = array('GLOBALS', '_FILES', '_COOKIE', '_POST', '_GET', '_SERVER', '_ENV', 'ignore');
// diff the ignore list as keys after merging any missing ones with the defined list
$vars = array_diff_key(get_defined_vars() + array_flip($ignore), array_flip($ignore));
// should be left with the user defined var(s) (in this case $testVar)
var_dump($vars);