3v4l.org

run code in 200+ php & hhvm versions
Bugs & Features
<?php $letter = 'a'; $aX = 1; $bX = "bb"; echo $${$letter . "X"};
based on lTfEh
Output for 5.6.0 - 5.6.30, hhvm-3.15.4, 7.0.0 - 7.3.0beta1
Notice: Undefined variable: 1 in /in/OQcc3 on line 8