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run code in 300+ PHP versions simultaneously
<?php session_set_save_handler( function() {return true;}, function() {return true;}, function() {return true;}, function() {return true;}, function() { $contents = ob_get_contents(); ob_end_clean(); print substr($contents, 0, 5); print ' PHP '; print substr($contents, 5); return true; }, function(){return true;} ); session_start(); ob_start(); echo 'Hello'; echo 'World';

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58.77 ms | 402 KiB | 5 Q