在dockerfile中的go build命令中注入或内插多个ENV变量

Question

I'm using a dockerfile to build go code, and I'm trying to pass 3 options in -ldflags option. Two of these flags comes from ENV variables, and I have to inject them in -ldflags content, thru string interpolation or concatenation, but I don't know how.

The objective is to inject git revision hash and current timestamp in two variables in main.go

It can be done by creating a file from dockerfile with "echo" command, but I want to be sure it's not possible with simple variables interpolation/concatenating

ENV GIT_REVISION $( git rev-parse --short HEAD )

ENV COMPILATION_TIMESTAMP $( date +%Y%m%dT%H:%M:%S )

RUN go get -d -v

// This one works:
RUN CGO_ENABLED=0 GOOS=linux go build -a -installsuffix cgo -ldflags '-extldflags "-static"' -o myprogram .

// This one, with those variables, fails:
RUN CGO_ENABLED=0 GOOS=linux go build -a -installsuffix cgo -ldflags "-extldflags '-static' -X main.compiledOn=${COMPILATION_TIMESTAMP} -X main.gitRevisionHash=${GIT_REVISION}" -o myprogram .

Answer 1

Unfortunately none of the current Docker builder command support environment variable replacement. Your best bet would be to write a shell script, where environment variable replacement is a first class citizen. Then, when you call RUN ./script you'll be able to catch the ENV values from the previous layers.