I have done the following

• I have searched the existing issues
• If possible, I've reproduced the issue using the 'main' branch of this project

Steps to reproduce

1. Create a Dockerfile like

ARG foo=ubuntu
FROM ${foo}:18.04
CMD ["/bin/bash", "-c", "sleep infinity"]

2. Build it with

container build --build-arg foo=bar .

Current behavior

Actual result is that ARG foo is not replaced and still contains the value ubuntu on the next line (FROM ...)

Expected Behavior

Expected result is that ARG foo gets replaced with value bar.

Environment

- OS: 
- Xcode: 
- Container: 0.1.0 (build: release, commit: 0fd8692)

Relevant log output

Code of Conduct

• I agree to follow this project's Code of Conduct