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<?php $var1 = "1"; $var2 = "2"; $temp1 = "var" . "5"; $temp2 = "var" . "2"; var_dump(${$temp5} ?? ${$temp2});
based on UginM
Output for 7.0.0 - 7.2.0
Notice: Undefined variable: temp5 in /in/lBYGr on line 7 string(1) "2"
Output for 5.3.19 - 5.6.21
Parse error: syntax error, unexpected '?' in /in/lBYGr on line 7
Process exited with code 255.