bug#81541: Script-breaking changes to "sum" command

"Fine, Thomas" via GNU coreutils Bug Reports <[email protected]>
writes:

> At some point between 8.3 and 9.5, the behavior of the sum command changed.
>
> It used to not print the filename, when only one file was checked.
> Now it always prints the filename no matter what.
>
> Scripts which compare checksums of individual files are now broken because
> they don't expect to see a filename there, and therefore the checksums of
> two different files no longer match.
>
> This is breaking scripts.  It should have been added as an option for the
> future to preserve script behavior, but, failing that, at least an option
> should have been added to make for a trivial fix for scripts.

It was changed in 9.0. The decision was not mine, but I feel that the
rationale is sound. Here is the NEWS entry:

   sum [-r] will output a file name, even if only a single name is passed.
   This is consistent with sum -s, cksum, and other sum(1) implementations.

That is, your script would be broken on NetBSD, DragonFlyBSD, FreeBSD,
macOS, and Solaris anyways. There are likely others that I am
unfortunately not able to test.

Regarding your scripts, you can have them use the following instead:

    $ sum < /dev/null
    00000     0

Alternatively, you can use 'cksum' which supports much better algorithms
which are less likely to have hash collisions.

Collin