Ignore stderr and use return code

[Chris Angelico]

On Mon, Oct 26, 2015 at 3:34 PM, Cameron Simpson <cs at zip.com.au> wrote:
> No. Mount should have a zero status if it succeeds and anon-zero exit status
> if it fails. There is no grey area here.

This is the general case. For specific programs, you can often check
their man pages; for the mount(8) on my system, it's bitwise:

       1      incorrect invocation or permissions
       2      system error (out of memory, cannot fork, no more loop devices)
       4      internal mount bug
       8      user interrupt
       16     problems writing or locking /etc/mtab
       32     mount failure
       64     some mount succeeded

It's also theoretically possible to get a return value of 127,
indicating that the 'mount' command was itself not found. That might
not seem likely, but if someone has a restricted $PATH, you might run
into that. Likewise 126 might indicate that "mount" exists but is
non-executable - again, unlikely in the case of mount, but possible.
In any case, you can generally depend on a non-zero exit status
indicating failure and zero being reserved for success.

ChrisA