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How to fix GitHub Actions error: "docker build" requires exactly 1 argument.

I've been working on migrating my the remote jobs platform I built in the past months from weremote.ro to weremote.eu.

The platform's backend is a GraphQL API built over Express.js which runs inside a Docker container. I was initially building the image myself, whenever I pushed some changes worth deploying to production, but I very quickly switched to GitHub Actions once I learned about this feature.

With this migration to .eu, I also added some features and most importantly, I moved a lot of config into env vars. So before I could actually deploy, I had to update main.workflow which is used by GitHub Actions to define the steps of the build process.

I went on and added the env vars, the secrets, and everything looked right. Except for the fact that I was getting this error when the build was running:

# [...] docker pull logs over here
"docker build" requires exactly 1 argument.
See 'docker build --help'.

Usage:  docker build [OPTIONS] PATH | URL | -

Build an image from a Dockerfile

### FAILED Build Docker image 13:23:26Z (41.66s)

I thought it was because I had a lot of build args that I was passing at build time.

Basically this:

args = "build --build-arg db_host=${DATABASE_HOST} --build-arg db_user=${DATABASE_USER} --build-arg db_pass=${DATABASE_PASSWORD} --build-arg db_name=${DATABASE_NAME} --build-arg database_authentication_source=${DATABASE_AUTHENTICATION_SOURCE} --build-arg cookie_signing_secret=${COOKIE_SIGNING_SECRET} --build-arg jwt_sign_key=${JWT_SIGN_KEY} --build-arg netlify_build_hook_url=${NETLIFY_BUILD_HOOK_URL} --build-arg mailgun_api_key=${MAILGUN_API_KEY} --build-arg bt_environment=${BT_ENVIRONMENT} --build-arg bt_merchant_id=${BT_MERCHANT_ID} --build-arg bt_public_key=${BT_PUBLIC_KEY} --build-arg bt_private_key=${BT_PRIVATE_KEY} --build-arg bt_merchant_account_id=${BT_MERCHANT_ACCOUNT_ID} -t ${IMAGE_NAME} ."

But as it turns out, my brain works better at 12:30 AM than it works at 2:00 PM.

While I was looking at the values of my env vars, I realised that two variables were storing strings with spaces — bad move.

So here's an example

$ SOME_ENV_VAR="This is a nice sentence!"
$ docker build --build-arg some_arg=${SOME_ENV_VAR} .

If this happens (and this is what happens when GitHub Actions set your env vars and secrets, you'll get this error:

[...]
"docker build" requires exactly 1 argument.
See 'docker build --help'.
[...]

That's because when interpreted the result is your sentence, but without the quotes:

echo $SOME_ENV_VAR
This is a nice sentence!

So when you run your docker build command, and pass the variable as a build argument, it looks like this:

docker build --build-arg some_arg=This is a nice sentence! .

That's a lot of arguments for docker build which it cannot identify.

And that, folks, is why you get weird errors when running docker build in GitHub Actions.

The solution

  1. You don't use phrases in your environment variables
  2. You add quotes around those variables

    • docker build --build-arg some_arg='${SOME_ENV_VAR}' .
    • Use single quotes because the whole "build" command is wrapped around with double quotes

Out!