Bash - Suppress Notice of Forked Command Being Killed

Question

Let's suppose I have a bash script (foo.sh) that in a very simplified form, looks like the following:

echo "hello"
sleep 100 &
ps ax | grep sleep | grep -v grep | awk '{ print $1 } ' | xargs kill -9
echo "bye"

The third line imitates pkill, which I don't have by default on Mac OS X, but you can think of it as the same as pkill. However, when I run this script, I get the following output:

hello
foo: line 4: 54851 Killed                  sleep 100
bye

My question is thus: how I suppress the line in the middle so that all I see is hello and bye?

Answer 1

ps ax | grep sleep | awk '{ print $1 } ' | xargs kill -9 2> /dev/null

EDIT: This is an answer for when the question was revised.

I'd suggest not using xargs.

kill -9 $(ps ax | grep sleep | grep -v grep | awk '{ print $1 } ')

Answer 2

The message is real. The code killed the grep process as well.

Run ps ax | grep sleep and you should see your grep process on the list.

What I usually do in this case is ps ax | grep sleep | grep -v grep

EDIT: This is an answer to older form of question where author omitted the exclusion of grep for the kill sequence. I hope I still get some rep for answering the first half.

Answer 3

How about disown? This mostly works for me on Bash on Linux.

echo "hello"
sleep 100 &
disown
ps ax | grep sleep | grep -v grep | awk '{ print $1 } ' | xargs kill -9
echo "bye"

Edit: Matched the poster's code better.

Answer 4

Have you tried to deactivate job control? It's a non-interactive shell, so I would guess it's off by default, but it does not hurt to try... It's regulated by the -m (monitor) shell variable.

Answer 5

While disown may have the side effect of silencing the message; this is how you start the process in a way that the message is truly silenced without having to give up job control of the process.

{ command & } 2>/dev/null

If you still want the command's own stderr (just silencing the shell's message on stderr) you'll need to send the process' stderr to the real stderr:

{ command 2>&3 & } 3>&2 2>/dev/null

To learn about how redirection works:

• From the BashGuide: http://mywiki.wooledge.org/BashGuide/TheBasics/InputAndOutput#Redirection
• An illustrated tutorial: http://bash-hackers.org/wiki/doku.php/howto/redirection_tutorial
• And some more info: http://bash-hackers.org/wiki/doku.php/syntax/redirection

And by the way; don't use kill -9.

I also feel obligated to comment on your:

ps ax | grep sleep | grep -v grep | awk '{ print $1 } ' | xargs kill -9

This will scortch the eyes of any UNIX/Linux user with a clue. Moreover, every time you parse ps, a fairy dies. Do this:

kill $!

(There is a reason why pkill, pgrep isn't in OS X: It's a broken tool by design.)