How to get PID of background process?

Question

I start background process from my shell script.
And I would like to kill this process when my script will be finished.
How to get pid of this process from my shell script?
As far as I can see variable $! contains pid of current script not background process.

Answer 1

You can use "jobs" command to get to a particular job.

Answer 2

The current script's pid is $$, the pid of the last background process is $!

Here's a sample transcript from a bash session (%1 refers to the ordinal number of background process as seen from jobs):

$ echo $$
3748

$ sleep 100 &
[1] 192

$ echo $!
192

$ kill %1

[1]+  Terminated              sleep 100

Answer 3

root@berlioz:/tmp# du -s / > x &
root@berlioz:/tmp# 
root@berlioz:/tmp# jobs
[1]+  Running                 du -s / > x &
root@berlioz:/tmp# ps
  PID TTY          TIME CMD
 3238 pts/1    00:00:00 du
 3241 pts/1    00:00:00 ps
 4562 pts/1    00:57:10 Xvfb
 4574 pts/1    00:00:00 dbus-launch
31990 pts/1    00:00:00 su
31998 pts/1    00:00:00 bash
32218 pts/1    00:00:04 metacity

Answer 4

You need to save the PID of the background process at the time you start it:

foo &
FOO_PID=$!
# do other stuff
kill $FOO_PID

You cannot use job control, since that is an interactive feature and tied to a controlling terminal. A script will not necessarily have a terminal attached at all so job control will not necessarily be available.