$ cat combo_not.txt | grep `printf linkedintrouble | sha1sum`
3ac85868a20c977661a12f770f0d116f87c74831
$ cat combo_not.txt | grep `printf nathanlinkedin | sha1sum`
a4d28368130ad555c77ec6a4dd18b8977ac0f589
$ cat combo_not.txt | grep `printf mypassword | sha1sum`
$ cat combo_not.txt | grep `printf yourpassword | sha1sum`
$ $ printf linkedintrouble | openssl sha1
(stdin)= 3ac85868a20c977661a12f770f0d116f87c74831
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
3ac85868a20c977661a12f770f0d116f87c74831 printf linkedintrouble |sha1sum |sed 's/ .*//' |grep -f - combo_not.txt