How do I safe git information in a file using GNU-make variables - gnu-make

Question

I want to save some git information in a textfile, which I want to put in the src folder of my project.
In case branch Master is checked out, I only want the date of the latest commit. If any other branch is checked out I want the date and the name of the branch like so:
date-branchname
This is my code:
src/version2.txt:
DATE=$(shell git log -1 --date=format:"%Y.%m.%d" --format="%ad")
BRANCH=$(shell git rev-parse --abbrev-ref HEAD)
ifeq ($(BRANCH), 'Master')
$(DATE) > $#
else
DATE+='-'
DATE+=$(BRANCH)
$(DATE) > $#
endif
I'm new to GNU make and quite confused with its syntax.
I assume my ifeq/else blocks are working fine, since I checked printing a dummy text to the version.txt file while having the Master or some other branch checked out.
I also saw my commands to get the date or the branch are ok, since I can put them to the textfile like so:
git log -1 --date=format:"%Y.%m.%d" --format="%ad" > $#
Only when I want to use variables, it seems the variable is empty, for example
$(DATE) > $#
seems to print an empty string to the textfile.
Also, I don't know if my way of creating the DATE-BRANCH output is correct at all.
I've spent ages trying and would really appreciate some help.
Thanks

Answer 1

You cannot create GNU make variables inside recipes and use them later in the GNU make file because GNU make first parses whole file and then runs recipes
You cannot use GNU make ifeqs inside recipes
% in command lines may cause problems in Windows, so I've added a workaround for it in the following code (skip it if your Makefile should work only for Unix-like systems)
' should not be used in ifeqs constants (GNU make reads it literaly)
src/version2.txt does not depend on anything and therefore will not be regenerated by GNU make (if it already exists), consider .PHONY for the target
Try this:
BRANCH:=$(shell git rev-parse --abbrev-ref HEAD)
ifeq ($(OS),Windows_NT)
P:=%%
else
P:=%
endif
.PHONY : src/version2.txt
ifeq ($(BRANCH),master)
src/version2.txt :
git log -1 --date=format:"$PY.$Pm.$Pd" --format="$Pad" >$#
else
src/version2.txt :
git log -1 --date=format:"$PY.$Pm.$Pd" --format="$Pad-$(BRANCH)" >$#
endif
Note that BRANCH will be computed each time you run make even if the src/version2.txt should not be regenerated.