length($foo)-grep(1+index(((1e9/.7)^7*13*89)."\_",$_),map chr($_),unpa
+ck"C*",$foo) == length("\Q$foo")-length($foo)
[download]

(since split and /./gs use regular expressions)

Replace == with != depending on whether you want what was asked for or something that matches the example code given. (: