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+ttn 2004-05-09
+
+The exit value of a program returning to the shell on unixoid systems is
+typically 0 for success, and non-0 (such as 1) for failure.  For vms it is
+odd (1,3,5...) for success, even (0,2,4...) for failure.
+
+This holds from the point of view of the "shell" (in quotes because vms has a
+different dispatch model that is not explained further here).
+
+From the point of view of the program, nowadays stdlib.h on both type of
+systems provides macros `EXIT_SUCCESS' and `EXIT_FAILURE' that should DTRT.
+
+NB: The numerical values of these macros DO NOT need to fulfill the the exit
+value requirements outlined in the first paragraph!  That is the job of the
+`exit' function.  Thus, this kind of construct shows misunderstanding:
+
+   #ifdef VMS
+      exit (1);
+   #else
+      exit (0);
+   #endif
+
+Values aside from EXIT_SUCCESS and EXIT_FAILURE are tricky.