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run code in 150+ php & hhvm versions
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<?php echo preg_replace_callback('/(_?[a-z]+)/', function($u) { var_dump($u); return str_replace('', '_', strtoupper($u[0])); } , 'rob_tr');
Output for 5.3.0 - 5.6.28, hhvm-3.10.0 - 3.12.0, 7.0.0 - 7.1.0
array(2) { [0]=> string(3) "rob" [1]=> string(3) "rob" } array(2) { [0]=> string(3) "_tr" [1]=> string(3) "_tr" } ROB_TR
Output for 4.4.2 - 4.4.9, 5.1.0 - 5.2.17
Parse error: syntax error, unexpected T_FUNCTION in /in/G0Cim on line 6
Process exited with code 255.
Output for 4.3.0 - 4.3.1, 4.3.5 - 4.4.1, 5.0.0 - 5.0.5
Parse error: parse error, unexpected T_FUNCTION in /in/G0Cim on line 6
Process exited with code 255.
Output for 4.3.2 - 4.3.4
Parse error: parse error in /in/G0Cim on line 6
Process exited with code 255.