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<?php $matches=array(); preg_match('/^(user/',"(user_data",$matches); var_dump($matches);
based on GgUlL
Output for 4.3.11 - 7.1.7
Warning: preg_match(): Compilation failed: missing ) at offset 6 in /in/JF0Tg on line 4 array(0) { }
Output for 4.3.0 - 4.3.10
Warning: Compilation failed: missing ) at offset 6 in /in/JF0Tg on line 4 array(0) { }