I'm running perl v5.8.0 on a redhat box and get the same errors as one4k4.

Unquoted string "a" may clash with future reserved word at ./sig.pl li
+ne 6.
Unquoted string "z" may clash with future reserved word at ./sig.pl li
+ne 6.

 |||||||
 [|0 0|]
  \ - /
   \=/
    ~
Subroutine main::p redefined at ./sig.pl line 6.
 y 4 p #
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HTH
Daeve