How do I wait for a background process to complete?

Question

I'm using Amazon Linux with bash shell. I would like to run a couple of processes in the background, and then wait for them to complete (either with a success or error exit code) before proceeding. So I tried:

node test.js 2>&1 | tee --append $TFILE1 &
proc1=$!
node SkyLocal.js 2>&1 | tee --append $TFILE2 &
proc2=$!

wait proc1
rc1=$?
wait proc2
rc2=$?

but I'm getting these errors:

/home/jboss/.jenkins/jobs/myproject/workspace/automated-tests/nodejs/run_tests.sh: line 36: wait: `proc1': not a pid or valid job spec
/home/jboss/.jenkins/jobs/myproject/workspace/automated-tests/nodejs/run_tests.sh: line 38: wait: `proc2': not a pid or valid job spec

How do I capture the PID of the background process and then wait for the process to complete before continuing?

Answer 1

As the error messages hint, the wait command won't try to look up the pid by the variable name for you (although as a built-in, it could theoretically do it).

You need to pass wait the actual pid values (or job numbers) as stored in the proc1 and proc2 variables. You do that by prepending $ to the variable names as usual. That will cause the shell to substitute the values for the variable names before passing them on to the wait command.