This (fairly long) one-liner counts the number of implementations of each hook in your Drupal installation:
ack "Implements? hook_" | perl -e 'while (<>) { m[(hook_\w+)] and $hooks{$1}++; } foreach (keys %hooks) { print "$_ - $hooks{$_}\n"; }'
To count only install file hooks, which was what I was doing, give ack the option "-G '.install'" thus:
ack "Implements? hook_" -G '.install' | perl -e 'while (<>) { m[(hook_\w+)] and $hooks{$1}++; } foreach (keys %hooks) { print "$_ - $hooks{$_}\n"; }'
You can probably adapt this for grep. Ack is far better though (proper regular expressions and sensible assumptions for starters).
Unfortunately, now I've taken ten minutes to do this, I've completely forgotten what I needed to count hooks for. So I'm posting this so by the time I remember I can come back to it!
Edit: Oh yes. I was generating a list of hooks implemented in .install files (just a list, the count is bonus) to check I'd covered everything in my patch for hook locations in the documentation.
