Find out the process id from a background running script

Question

Hello all:
I created a java service and use a shell script to drive it from background. In the script, I have code like this:
javac myApp & I want to find out the pid for this process. After googling for a while I came up with this:
echo $$ > test.pid However, I notice two things:
1. This only works when my script runs frontground, meaning only when I remove "&";
2. The pid file, test.pid, won't be created until the running script exits, after I clicked ctrl+c, for instance.
Now the question is, how can I find out the pid of a background running script from within the script itself?
I don't want to use code such as ps -ef | grep .... because of the possible name conflict.
Thanks,
Johnny

Answer 1

Yes, but as far as I understand this can happen to any background process, for instance, when the user logs out while a background process is still running.
But using the "$!" variable as you've shown is the "correct" solution.
This is probably what the OP is looking for:
javac myApp & echo $! > test.pidFrom the bash man page:
$ Expands to the process ID of the shell. In a () subshell, it expands to the process ID of the current shell, not the subshell.
! Expands to the process ID of the most recently executed background (asynchronous) command.