Warning: Undefined variable $XOR in index.php(23) : eval()'d code(1) : eval()'d code on line 35

[0xS4D]

When I'm trying to obfuscate my file, had a problem with variables u.u

this is the error:

Warning: Undefined variable $XOR in index.php(23) : eval()'d code(1) : eval()'d code on line 35

there is any way to scape variables?