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<?php /*echo preg_replace_callback('/([a-z]+)(_[a-z]+)/', function($u) { var_dump($u); return ucwords(str_replace('_', '', $u[1])); } , 'rob_tr_yuui'); */ echo preg_replace('/([a-z])(_[a-z])/', '$1.$2', 'rob_tr_yuui');
Output for 4.3.0 - 7.1.0
rob._tr._yuui