can't capture PID from background process started in a sub-shell that's running in a heredoc passed to `sudo su`

Question

I'm trying to capture the PID of a process started in a sub-shell so I can check if the process started correctly, the process in question is a puma app.

sudo su - $APPUSER <<-BASH
    PID="\$(bundle exec puma -C config/puma.rb)"

    "\$(bundle exec puma -C config/puma.rb & export PID=$1)"

    "\$(bundle exec puma -C config/puma.rb &)"

    PID="\$(ps aux | grep \"[p]uma.*[u]nix.*$APPNAME\" | awk '{ print \$2}')"
BASH

and it returns nothing, weirdly, if I do any of those without a surrounding "" I get this error:

-bash: line 22: [26740]: command not found

the number in the [] is the pid, I know this because I get this when I run the script again (I check if the pid exists):

app is running with pid: 26740

I think this is happening because I'm doing the commands in a heredoc and passing them to sudo su

How do I get the pid from the background process I started in a sub-shell.

Answer 1

You can't overwrite internal PID value. Use lowercase environment variables.