Learn more about Docker ARG substitution from our experts. Our Docker Support team is here to help you with your questions and concerns.

About Docker ARG substitution

Docker ARG sub is a useful feature in Docker that makes it easy to pass values to our Dockerfile at build time.

ARGs can be described as variables that we can set in the Dockerfile with the ARG command as seen below:

ARG VARIABLE_NAME

Furthermore, when we build an image via docker build, we can pass a value for the ARG as seen here:

docker build --build-arg VARIABLE_NAME=value

Then, we can reference the value of the ARG with the syntax ${VARIABLE_NAME} as seen below:

ENV ENV_VAR ${VARIABLE_NAME}

After the above command, the ENV_VAR’s value is set to the value of the VARIABLE_NAME ARG.

Furthermore, ARG sub is handy when it comes to parameterizing Docker builds and making them more flexible. It also allows us to pass values to our Dockerfile at build time, without hardcoding them in the file itself.

Let us know in the comments if you need further help with Docker ARG substitution.

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Conclusion

To sum up, our Support Techs introduced us to Docker ARG substitution and why it is beneficial.