Get PID of a function executed in the background

Question

#!/bin/bash

function abc() # wait for some event to happen, can be terminated by other process
{
    sleep 3333 
}

echo "PID: $$"
abc &
echo "PID: $$"

I need to retrieve the pid of this function, but the echo prints the same string.

If I'm not going to put abc() out of this script, is it possible to get it's pid and terminate that function?

This question is very similar to How to get the pid of the last executed command in shell script?. The only essential difference is that this questions is asking about a function. But, as it turns out, it doesn't make the answer different (the function is executed in a backgrounded subshell). — imz -- Ivan Zakharyaschev, Jun 02 '15 at 14:06

score 18 · Accepted Answer · edited Nov 26 '12 at 02:59

You have two options, I think:

$BASHPID or $!

echo "version: $BASH_VERSION"
function abc() # wait for some event to happen, can be terminated by other process
{
          echo "inside a subshell $BASHPID" # This gives you the PID of the current instance of Bash.
          sleep 3333
}

echo "PID: $$" # (i)
abc &
echo "PID: $$" # (ii)
echo "another way $!" # This gives you the PID of the last job run in background
echo "same than (i) and (ii) $BASHPID" # This should print the same result than (i) and (ii)

sh-4.2$ ps ax|grep foo
25094 pts/13   S      0:02 vim foo.sh
25443 pts/13   S+     0:00 grep foo

sh-4.2$ ./foo.sh
version: 4.2.39(2)-release
PID: 25448
PID: 25448
another way 25449
same than (i) and (ii) 25448
inside a subshell 25449

sh-4.2$ ps ax|grep foo
25094 pts/13   S      0:02 vim foo.sh
25449 pts/13   S      0:00 /bin/bash ./foo.sh
25452 pts/13   S+     0:00 grep foo

Cheers,

Source: http://tldp.org/LDP/abs/html/internalvariables.html

As my test, normally $! is enough to get the single background process PID, sometimes if i run multiple background child processes (run as function following by &), it will only able to get accurate child PID with $BASHPID, especially when you want to retrieve child process itself PID inside your child process which running in background, e.g function my_func() { echo $BASHPID .... } will print accurate PID for my_func, if we run as my_func arg1 arg2 ... & — Lampard, Jul 24 '20 at 01:19

David Bain · Answer 2 · 2012-11-26T09:50:12.003

4

I think you're looking for the $!

function abc() # wait for some event to happen, can be terminated by other process
{
    sleep 3333 
}

echo "PID: $$"
abc &
echo "PID: $!"

edited Nov 26 '12 at 09:50

answered Nov 26 '12 at 02:35

David Bain

151
3

“!$”? Is that $! with a typo? – manatwork Nov 26 '12 at 09:01
@manatwork yes. Fixed now. – David Bain Nov 26 '12 at 09:50

Get PID of a function executed in the background

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