Stop grep after Nth files matched

Question

I have many files I need to search for some string. I'm using grep -rl 'pattern' * to find files that contain the pattern. However, I'm only interested in file count - if string occurs in more than N files, I want grep to stop immediately after hitting Nth match(as searching through the whole file hierarchy is long operation). It would be nice if it returned some meaningful exit code, but if that's impossible then I can just pipe it to wc without a problem.

How can I tell grep to stop searching other files after matching Nth file?

Answer 1

You can pipe grep result to head.

Note, that in order to ensure stopping after Nth match, you need to using stdbuf to make sure grep don't buffer its output:

stdbuf -oL grep -rl 'pattern' * | head -n10

As soon as head consumed 10 lines, it terminated and grep will receive SIGPIPE because it still output something to pipe while head was gone.

This assumed that no file names contain newline.

Answer 2

While this isn't exactly what you asked, I think this may suit your needs considering that using the count of the files can make your script time vary depending on the size of the files, etc, and seeing as how you are trying to limit processor time, you could

timeout -k 1m grep -rl 'pattern' *

This, rather than count how many files are processed to keep the script running fast, will actually shut the command down after an alloted period of time has passed. In my code example, it is 1 minute but that can be changed to seconds (s) hours (h) or even days (d) by replacing the 1m with the correct respective suffex. For example, let's let it run for an hour...

timeout -k 1h grep -rl 'pattern' *

I hope this helps someone!

Answer 3

Not pure grep, but with bash:

i=0
grep -rl 'pattern' * | while read l ; do
  i=$(($i+1))
  echo $l
  if [ $i -ge N ] ; then 
    echo "at least N matches"
    break
  fi
done

Will be faster if you have far more files matching than your threshold of N matches.