The $! variable is actually used for system error messages. The version of perl doesn't really matter; it's the OS and platform that determine whether or not this JAPH will produce the proper output.

For example, on a machine running RedHat linux, I get:

substr outside of string at tmp.pl line 14.
Use of uninitialized value in concatenation (.) or string at tmp.pl li
+ne 14.
substr outside of string at tmp.pl line 14.
Use of uninitialized value in concatenation (.) or string at tmp.pl li
+ne 14.
J edretig  no hial
[download]

And on another machine running IRIX, I get: J eemp tocrdrnots i f I'm afraid it just doesn't make sense to rely on the value of $! for a JAPH.