How to get PID of last process run from bash script?

Question

I am trying to get the process ID of the last executed command from within a bash script. Normally I would do:

$ nohup ./test > nhout &
nohup: redirecting stderr to stdout
$ echo $!
3006196 #This is the PID

I am trying to do the exact same thing from within a shell script.

#!/bin/bash
for i in {1..10};do
    `nohup ./testscript_${i} > nhout_${i} &`
    echo $! >> pid_list.txt
done

However, when I check pid_list.txt, the file is empty. I understand this could be because $! refers to the script that I ran rather than the nohup command. But I don't know how to fix this and couldn't find any resources online either. How would I achieve this?

Answer 1

You've got a pair of incorrect backticks surrounding the nohup command. What's happening as a result is that you're executing the (empty) output from the nohup. The nohup command is being run only as a side-effect to generate output for the backticks to execute.

Try this instead:

#!/bin/bash
for i in {1..10}; do
    nohup "./testscript_$i" > "nhout_$i" &
    echo "$!" >> pid_list.txt
done