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?

Solution

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.

Comments

[PSkocik]

wait $proc1 Don't forget the dollar sign.