code.delx.au - gnu-emacs/blob - admin/notes/exit-value

   1 ttn 2004-05-09
   2
   3 The exit value of a program returning to the shell on unixoid systems
   4 is typically 0 for success, and non-0 (such as 1) for failure. This is
   5 not always the case on other systems.
   6
   7 From the point of view of the program stdlib.h provides macros
   8 `EXIT_SUCCESS' and `EXIT_FAILURE' that should DTRT.  N.B. The
   9 numerical values of these macros DO NOT need to fulfill the exit value
  10 requirements outlined in the first paragraph!  That is the job of the
  11 `exit' function.  Thus, this kind of construct shows misunderstanding:
  12
  13    #ifdef WEIRD_OS
  14       exit (1);
  15    #else
  16       exit (0);
  17    #endif
  18
  19 Values aside from EXIT_SUCCESS and EXIT_FAILURE are tricky, but can be
  20 used to indicate finer gradations of failure.  If this is the only
  21 information available to the caller, clamping such values to
  22 EXIT_FAILURE loses information.  If there are other ways to indicate
  23 the problem to the caller (such as a message to stderr) it may be ok
  24 to clamp.  In all cases, it is the relationship between the program
  25 and its caller that must be examined.
  26
  27 [Insert ZAMM quote here.] <-- I presume this refers to ``Zen and the
  28 Art of Motorcycle Maintenance'' - Reuben Thomas <rrt@sc3d.org>.