Nested ifndef in Makefile - makefile

Question

In my Makefile I am trying to step through different ways of programatically setting an environment variable in a target. However, each statement inside each ifndef appears to be being executed every time. How do I get around this happening?
repository:
ifndef REPOSITORY_URI
#$(eval REPOSITORY_URI := $(shell bash -c "aws --region $(REGION) ecr describe-repositories --repository-names $(APP) | jq -r '.repositories[0].repositoryUri'"))
ifndef REPOSITORY_URI
#$(eval REPOSITORY_URI := $(shell bash -c "aws --region $(REGION) ecr create-repository --repository-name $(APP) | jq -r '.repositories[0].repositoryUri'"))
ifndef REPOSITORY_URI
echo "Could not establish link to AWS Repository, please ensure your credentials are set and try again"
endif
endif
endif

Answer 1

You're trying to compute a value for the make-variable REPOSITORY_URI using
make-functions, but you mistakenly believe that computing a value for a make-variable calls for a make-target and a recipe.
The actual meaning of your recipe for repository is quite different from what
you think and explaining what it does mean would be a large digression, since
no target or recipe is needed. To do what you are after here, just write:
ifndef REPOSITORY_URI
REPOSITORY_URI := $(shell bash -c "aws --region $(REGION) ecr describe-repositories --repository-names $(APP) | jq -r '.repositories[0].repositoryUri'")
ifndef REPOSITORY_URI
REPOSITORY_URI := $(shell bash -c "aws --region $(REGION) ecr create-repository --repository-name $(APP) | jq -r '.repositories[0].repositoryUri'")
ifndef REPOSITORY_URI
$(error "Could not establish link to AWS Repository, please ensure your credentials are set and try again")
endif
endif
endif
at the place in your makefile where you want to assign a value to REPOSITORY_URI
(or fail).
This by itself now constitutes a makefile with no targets. But presumably you
want to use the value of REPOSITORY_URI in the recipe for one or more targets, e.g.
ifndef REPOSITORY_URI
REPOSITORY_URI := $(shell bash -c "aws --region $(REGION) ecr describe-repositories --repository-names $(APP) | jq -r '.repositories[0].repositoryUri'")
ifndef REPOSITORY_URI
REPOSITORY_URI := $(shell bash -c "aws --region $(REGION) ecr create-repository --repository-name $(APP) | jq -r '.repositories[0].repositoryUri'")
ifndef REPOSITORY_URI
$(error "Could not establish link to AWS Repository, please ensure your credentials are set and try again")
endif
endif
endif
.PHONY: all
all:
echo REPOSITORY_URI=$(REPOSITORY_URI)
I recommend the GNU Make documentation