[uselessuseof]

does your grep have an -f option?

   printf linkedintrouble |sha1sum |sed 's/ .*//' |grep -f - combo_not.txt

[spal]

If you look where we started ( http://news.ycombinator.com/item?id=4076559 ), I'm not trying to feed the regex pattern to grep via stdin, but I'm trying to feed the input stream to be searched for the pattern to grep via stdin.