how to wait for "docker exec " to complete before continue in shell script

Question

I have a docker exec command, and I want to wait for it to complete before continuing the rest of a shell script, how do I accomplish that?

#!/bin/bash
docker exec -it debian sleep 10;

wait
echo done

Update: should not use -it option

#!/bin/bash
docker exec debian sleep 10;

wait
echo done

That should be the normal shell behavior. Do you have some evidence that it’s not working? — David Maze
– David Maze, Commented Jul 3, 2019 at 14:43
Running docker exec ... sleep 10 against a container I have running on my system definitely takes 10 seconds before it returns. — David Maze
– David Maze, Commented Jul 3, 2019 at 14:53
It's the default behavior. Docker exec waits for the command to complete. — Prakash Krishna
– Prakash Krishna, Commented Jul 3, 2019 at 14:56

BMitch · Accepted Answer · 2019-07-03 15:19:46Z

The docker exec command will wait until it completes by default. The possible reasons for docker exec to return before the command it runs has completed, that I can think of, are:

You explicitly told docker exec to run in the background with the detach flag, aka -d.
The command you are exec'ing inside the container returns before a process it runs has completed, e.g. launching a background daemon. In that scenario, you need to adjust the command you are running.

Here are some examples:

$ # launch a container to test:
$ docker run -d --rm --name test-exec busybox tail -f /dev/null
a218f90f941698960ee5a9750b552dad10359d91ea137868b50b4f762c293bc3

$ # test a sleep command, works as expected
$ time docker exec -it test-exec sleep 10

real    0m10.356s
user    0m0.044s
sys     0m0.040s

$ # test running without -it, still works
$ time docker exec test-exec sleep 10

real    0m10.292s
user    0m0.040s
sys     0m0.040s

$ # test running that command with -d, runs in the background as requested
$ time docker exec -itd test-exec sleep 10 

real    0m0.196s
user    0m0.056s
sys     0m0.024s

$ # run a command inside the container in the background using a shell and &
$ time docker exec -it test-exec /bin/sh -c 'sleep 10 &'

real    0m0.289s
user    0m0.048s
sys     0m0.044s

smallbee · Accepted Answer · 2019-07-03 14:59:07Z

3

Update: should not use -it option. This should work.

#!/bin/bash
docker exec debian sleep 10;

wait
echo done

answered Jul 3, 2019 at 14:59

smallbee

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