How to get PID from forked child process in shell script

Question

I believe I can fork 10 child processes from a parent process.

Below is my code:

#/bin/sh fpfunction(){     n=1     while (($n<20))     do         echo "Hello World-- $n times"         sleep 2         echo "Hello World2-- $n times"         n=$(( n+1 ))     done }  fork(){     count=0     while (($count<=10))     do         fpfunction &         count=$(( count+1 ))     done }  fork 

However, how can I get the pid from each child process I just created?

Answer 1

The PID of a backgrounded child process is stored in $!.

fpfunction & child_pid=$! parent_pid=$$ 

For the reverse, use $PPID to get the parent process's PID from the child.

fpfunction() {     local child_pid=$$     local parent_pid=$PPID     ... } 

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Also for what it's worth, you can combine the looping statements into a single C-like for loop:

for ((n = 1; n < 20; ++n)); do do     echo "Hello World-- $n times"     sleep 2     echo "Hello World2-- $n times" done 

Answer 2

From the Bash manual:

!

Expands to the process ID of the most recently executed background (asynchronous) command.

i.e., use $!.