The Dockerfile documentation is missing information on variable replacement

[SetTrend]

Is this a docs issue?

• My issue is about the documentation content or website

Type of issue

I can't find what I'm looking for

Description

At this time, it's hard if even impossible to tell where variable replacement is taking place: Is it in the Docker engine or is it in the container's shell?

I'm working with a Windows container here, and the default Windows shell is cmd. For variable replacement to occur in this shell, I need to write %varName% instead of $varName.

The Dockerfile documentation doesn't provide information on which type of variable replacement syntax applies for the different Dockerfile instructions. So, it's a continuous, cumbersome try-and-error loop for me to finally reach the correct syntax.

Location

https://docs.docker.com/reference/dockerfile/

Suggestion

Please add a corresponding note to each of the commands what kind of variable replacement is taking place. (I.e., Docker engine syntax or shell syntax.)