Question

I want to write a shell script (.sh file) to get a given process id. What I’m trying to do here is once I get the process ID, I want to kill that process. I’m running on Ubuntu (Linux).

I was able to do it with a command like

ps -aux|grep ruby
kill -9 <pid>

but I’m not sure how to do it through a shell script.

Answer 1

Using grep on the results of ps is a bad idea in a script, since some proportion of the time it will also match the grep process you’ve just invoked. The command pgrep avoids this problem, so if you need to know the process ID, that’s a better option. (Note that, of course, there may be many processes matched.)

However, in your example, you could just use the similar command pkill to kill all matching processes:

pkill ruby

Incidentally, you should be aware that using -9 is overkill (ho ho) in almost every case – there’s some useful advice about that in the text of the “Useless Use of kill -9 form letter “:

No no no. Don’t use kill -9.

It doesn’t give the process a chance to cleanly:

1. shut down socket connections
2. clean up temp files
3. inform its children that it is going away
4. reset its terminal characteristics

and so on and so on and so on.

Generally, send 15, and wait a second or two, and if that doesn’t
work, send 2, and if that doesn’t work, send 1. If that doesn’t,
REMOVE THE BINARY because the program is badly behaved!

Don’t use kill -9. Don’t bring out the combine harvester just to tidy
up the flower pot.