CODEWITHSUNDEEP
bashdockerdocker-composedockerfile
Federico Bellini
Federico Bellini

Reputation: 514

docker run entrypoint with multiple commands

How can I have an entrypoint in a docker run which executes multiple commands? Something like:

docker run --entrypoint "echo 'hello' && echo 'world'" ... <image>

The image I'm trying to run, has already an entrypoint set in the Dockerfile, so solution like the following seems not to work, because it looks my commands are ignored, and only the original entrypoint is executed

docker run ... <image> bash -c "echo 'hello' && echo 'world'"

In my use-case I must use the docker run command. Solution which change the Dockerfile are not acceptable, since it is not in my hands

Upvotes: 7

Views: 19419

Answers (1)

David Maze
David Maze

Reputation: 159830

As a style point, this gets vastly easier if your image has a CMD that can be overridden. If you only need to run one command with no initial setup, make it be the CMD and not the ENTRYPOINT:

CMD ./some_command  # not ENTRYPOINT

If you need to do some initial setup and then launch the main command, make the ENTRYPOINT be a shell script that ends with the special instruction exec "$@". The CMD will be passed into it as parameters, and this line replaces the shell script with that command.

#!/bin/sh
# entrypoint.sh
... do first time setup, run database migrations, set variables ...
exec "$@"

# Dockerfile
...
ENTRYPOINT ["./entrypoint.sh"] # MUST be JSON-array syntax
CMD ./some_command             # as before

If you do these things, then you can use your initial docker run form. This will replace the CMD but leave the ENTRYPOINT intact. In the wrapper-script case, your alternate command will be run as the exec "$@" command, so all of the first-time setup will be done first.

# Assuming the image correctly honors the CMD
docker run ... \
  image-name \
  sh -c 'echo "foo is $FOO" && echo "bar is $BAR"'

If you really can't do this, you can override the docker run --entrypoint. This runs instead of the image's entrypoint (if you want the image's entrypoint you have to run it yourself), and the syntax is awkward:

# Run a shell command instead of the entrypoint
docker run ... \
  --entrypoint /bin/sh \
  image-name \
  -c 'echo "foo is $FOO" && echo "bar is $BAR"'

Note that the --entrypoint option comes before the image name, and its arguments come after the image name.

Upvotes: 21

Related Questions