In a Makefile, how can I fetch and assign a git commit hash to a variable?

Question

A make all clones the git repo. I want to know what the commit hash is and assign the git commit hash to a variable which can be used later in the Makefile

e.g.

all: download
      echo '$(GIT_COMMIT)'

download:
      cd buildarea && git clone [email protected]:proj/project.git
      $(eval GIT_COMMIT = $(shell cd buildarea/project && git log -l --pretty=format:"%H"))
      echo '$(GIT_COMMIT)'

Answer 1

How about use shell function and 2 targets for it?

all: download getver

getver: VER=$(shell cd buildarea/project && git log -1 --pretty=format:"%H")
getver:
        @echo GIT_COMMIT=$(VER)

download:
        mkdir -p buildarea && cd buildarea && [email protected]:proj/project.git

Answer 2

Because of the way that make evaluates the target the git clone executes after $(shell), so cd tries to move to a directory that doesn't exist yet. What you can do is simply perform the whole act in a single $(shell) call.

all: download
      echo '$(GIT_COMMIT)'

download:
      $(eval GIT_COMMIT = $(shell git clone [email protected]:proj/project.git buildarea/project && cd buildarea/project && git rev-parse HEAD))
      echo '$(GIT_COMMIT)'