Docker environment variable in ENTRYPOINT array?

In this article, we will see how to effectively use Docker environment variables within the ENTRYPOINT array, which allows greater flexibility and control over container execution.

Define the environment variables

To set environment variables in Docker, you can use the -e or --env flag while running the docker run command.

docker run -e VARIABLE_NAME=variable_value image_name

The above command sets the environment variable VARIABLE_NAME with the value variable_value within the container.

Using env variables in ENTRYPOINT:

In the Dockerfile, The ENTRYPOINT instruction allows us to configure a command executed when the container starts. We can pass arguments to the ENTRYPOINT command, making it a powerful tool for container configuration. To utilize environment variables within the ENTRYPOINT array:

Define the environment variable in the docker file with the default value.

Within the Dockerfile, specify the desired environment variables using the ENV instruction. The following sets the environment variable VARIABLE_NAME with the default value default_value.

ENV VARIABLE_NAME=default_value

Reference environment variables in the ENTRYPOINT array

In the ENTRYPOINT array, we can reference the environment variables using the standard shell syntax ($VARIABLE_NAME). The #VARIABLE_NAME will be replaced during the runtime.

ENTRYPOINT ["executable", "$VARIABLE_NAME", "arg1", "arg2"]

When running the container, you can use the -e flag to override the default value of an environment variable.

docker run -e VARIABLE_NAME=new_value image_name