bug#10355: Add an option to {md5,sha*} to ignore directories

[Gilles Espinasse]

I was using a way to check md5sum on a lot of file using
 for myfile in `cat ${ALLFILES}`; do if [ -f /${myfile} ]; then md5sum
/$myfile >> $ALLFILES}.md5; fi; done

But this is slow, comparing with xargs md5sum way.
time (for myfile in `cat ${ALLFILES}`; do if [ -f /${myfile} ]; then md5sum
/$myfile >> ${ALLFILES}.md5; fi; done)

real    0m26.907s
user    0m40.019s
sys     0m10.253s

This is faster using xargs md5sum.
time (sed -e '/.\/$/d' -e 's|^.|/&|g' ${ALLFILES} | xargs md5sum
>${ALLFILES}.md5)
md5sum: /etc/ipsec.d/cacerts: Is a directory
md5sum: /etc/ipsec.d/certs: Is a directory
md5sum: /etc/ipsec.d/crls: Is a directory
md5sum: /etc/ppp/chap-secrets: No such file or directory
md5sum: /etc/ppp/pap-secrets: No such file or directory
md5sum: /etc/squid/squid.conf: No such file or directory

real    0m1.176s
user    0m0.780s
sys     0m0.400s

That run mostly 30 times faster.
In the above example, I already skipped most of the directories in the list,
removing lines that end with / but not all directories in my list match on
that condition.

So the fast solution emit errors and end with status 123.
I know I could hide error messages and status error but that start to be
ugly.
sed -e'/.\/$/d' -e 's|^.|/&|g' ${ALLFILES} | xargs md5sum > ${ALLFILES}.md5
2>/dev/null || test $? -eq 123

Would it not be great to support an option in {md5,sha*} to ignore directory
error?
I may even be able to produce a patch if there is a real interest.

Gilles