Are you wanting to try and grep "HOOK" on a line by itself, or specifically just the first match?
There are all sorts of things that you could actually want to know, although I am not sure which you are wanting. What exactly is it that you are needing to do?
# grep a file, return first result and stop
grep -m1 "HOOK" file.txt
# grep a file, only return result with HOOK on line by itself
grep -P "^HOOK$" file.txt
# you can also use egrep (or instead of -P use pgrep)