bug#15604: sha256sum (and others of the *sum family) lacks important option

[Hadmut Danisch]

Hi,

the hashsum check files like  sha256sum would be quite usefull (and
improve security), if they could easily be used within shellscripts to
verify downloads. E.g. Ubuntu provides signed hash files like

http://releases.ubuntu.com/precise/SHA256SUMS
http://releases.ubuntu.com/precise/SHA256SUMS.gpg


But one rarely downloads all files, only the needed ones.

Unfortunately, sha256sum prints warnings and exits with exit status 1
when files are missing, even when the present files are correct. This
makes checking the files more difficult in shellscripts and might keep
most script authors from checking downloads.

It would be significantly more usefull and thus more secure if  the *sum
commands had an additional option to not report missing files as an
error and to verify just the present files.

regards
Hadmut