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run code in 200+ php & hhvm versions
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<?php var_dump(preg_replace('{^(\\\\.+)\\\\[^\\\\]+$|^([^\\\\]+)\\\\[^\\\\]+$}', '$1', '\\Grapa'));
based on mqmcs
Output for 4.3.0 - 7.2.0
string(6) "\Grapa"