$ printf linkedintrouble | openssl sha1
Yes, I've read http://partmaps.org/era/unix/award.html#cat . The output of sha1sum already contains a trailing '-' which is something I wanted to feed into 'grep' using command substitution, so that 'grep' can now just accept the input stream from 'stdin'. Now, how do you feed the input to grep via 'stdin' if you don't want to use 'cat'?
$ printf linkedintrouble | openssl sha1 | cut -c10- | grep -f - combo_not.txt
printf linkedintrouble |sha1sum |sed 's/ .*//' |grep -f - combo_not.txt