Buildspec file, pass env var to Dockerfile?

Hi, I have a buildspec file. In prebuild I got: pre_build: commands: IMAGE_TAG=$(cd src && git rev-parse HEAD | cut -c 1-7)

Then I have a build phase and in Dockerfile I have command go build, how to pass it rev-parse HEAD from pre_build to Dockerfile?

Dockefile is building in a separate container which is not seeing git rev-parse HEAD from pre_build phase.

RUN go build -v -ldflags=" -X 'main.BuildSha=$(git rev-parse HEAD)'"