3v4l.org

run code in 200+ php & hhvm versions
Bugs & Features
<?php echo strtolower(preg_replace('/(?!^)[[:upper:]]+/', '_$0', 'isAa_BB CcDd'));
Output for 4.3.0 - 5.6.30, hhvm-3.10.1 - 3.15.4, 7.0.0 - 7.3.1
is_aa__bb _cc_dd