How to run a program and know its PID in Linux?

Question

How to run a program and know its PID in Linux?

If I have several shells running each other, will they all have separate PIDs?

Answer 1

Greg's wiki to the rescue:

• $! is the PID of the last backgrounded process.
• kill -0 $PID checks whether $PID is still running. Only use this for processes started by the current process or its descendants, otherwise the PID could have been recycled.
• wait waits for all children to exit before continuing.

Actually, just read the link - It's all there (and more).

$$ is the PID of the current shell.

And yes, each shell will have its own PID (unless it's some homebrewed shell which doesn't fork to create a "new" shell).

Answer 2

1) There is a variable for that, often $$:

edd@max:~$ echo $$                  # shell itself
20559
edd@max:~$ bash -c 'echo $$'        # new shell with different PID
19284
edd@max:~$ bash -c 'echo $$'        # dito
19382
edd@max:~$ 

2) Yes they do, the OS / kernel does that for you.