CVS--Concurrent Versions System v18.104.22.168
A.2 CVS's exit status
CVS can indicate to the calling environment whether it
succeeded or failed by setting its exit status.
The exact way of testing the exit status will vary from
one operating system to another. For example in a unix
shell script the `$?' variable will be 0 if the
last command returned a successful exit status, or
greater than 0 if the exit status indicated failure.
If CVS is successful, it returns a successful status;
if there is an error, it prints an error message and
returns a failure status. The one exception to this is
cvs diff command. It will return a
successful status if it found no differences, or a
failure status if there were differences or if there
was an error. Because this behavior provides no good
way to detect errors, in the future it is possible that
cvs diff will be changed to behave like the
other CVS commands.