Iterating the values of a submake - makefile

Question

I'm trying to automate some commands I use regularly in a Makefile, but I can't seem to figure out the right syntax for it.
Given the following targets:
.PHONY: params-list
params-list:
#aws ssm get-parameters-by-path --path /${SERVICE}/${ENV} | jq -c -r '.Parameters[] | .Name'
.PHONY: params-get
params-get:
#aws ssm get-parameter --name ${PARAM} --with-decryption | jq -c -r .Parameter.Value
I was attempting to call params-list and then feed the results into params-get. My best attempt was along the lines of:
.PHONY: params
params:
for param in $(MAKE) params-list; do \
$(MAKE) params-get PARAM=$${param}; \
done
But obviously doesn't work. What's the right way of achieving this?

Answer 1

One hint is to eschew shell constructs for make ones. Going one step at a time here.
For the get operation, we encode one target for each param. So for param p1 (say), we invent a target params-get<p1>. We note that inside the recipe (i.e., the shell commands) that $# will expand to params-get<p1>. Therefore ${#:params-get<%>=%} will expand to p1.
Writing this out in make syntax:
.PHONY: params-get<p1>
params-get<p1>:
#aws ssm get-parameter --name ${#:params-get<%>=%} --with-decryption | jq -c -r .Parameter.Value
I note that with an intermediate variable we can have exactly the same recipe you used in your earlier incantation.
PARAM = ${#:params-get<%>=%}
.PHONY: params-get<p1>
params-get<p1>:
#aws ssm get-parameter --name ${PARAM} --with-decryption | jq -c -r .Parameter.Value
If we have a second param pa (say), that's easy to add:
PARAM = ${#:params-get<%>=%}
.PHONY: params-get<p1> params-get<pa>
params-get<p1> params-get<pa>:
#aws ssm get-parameter --name ${PARAM} …
I hope you can see some boiler plate appearing here.
Moving towards some more dynamically generated make, rather than hard-coding each param, let's put all the possible params in a list called $PARAMS
PARAMS := p1 pa another
get-targets := ${PARAMS:%=params-get<%>}
PARAM = ${#:params-get<%>=%}
.PHONY: ${get-targets}
${get-targets}:
#aws ssm get-parameter --name ${PARAM} …
.PHONY: params-get
params-get: ${get-targets}
echo $# Done
I have added your original params-get target. Now all the work is done by dependencies.
No shell loop in sight.
The exit code of each aws ssm get-parameter is checked by make.
The code is parallel safe: make -j9 will run 9 jobs in parallel until the work is exhausted. Nice if you have 8 CPUs. (If your make is not parallel safe then it is broken by the way.)
We are pretty close now. We just have to ensure $PARAMS is set to the output of ssm get-parameters-by-path.
Something like:
.PHONY: params-list
params-list:
#aws ssm get-parameters-by-path --path /${SERVICE}/${ENV} | jq -c -r '.Parameters[] | .Name'
PARAMS := $(shell ${MAKE} params-list)
get-targets := ${PARAMS:%=params-get<%>}
PARAM = ${#:params-get<%>=%}
.PHONY: ${get-targets}
${get-targets}:
#aws ssm get-parameter --name ${PARAM} --with-decryption | jq -c -r .Parameter.Value
.PHONY: params-get
params-get: ${get-targets}
echo $# Done
Definitely not a fan of using $(shell …), but this is just a sketch.

Answer 2

You could do a single (long) target/recipe as follows:
.PHONY: params-get
params-get:
#for p in $$(aws ssm get-parameters-by-path --path /${SERVICE}/${ENV} | jq -c -r '.Parameters[] | .Name'); do \
aws ssm get-parameter --name $$p --with-decryption | jq -c -r .Parameter.Value; \
done
This assumes that your parameters don't have white spaces in them
------------ EDIT ---------------
To be able to access the parameters in another recipe, you can create a rule to create a file with the list of files in one recipe, and then access that file in another recipe as so:
# note that in this case .params-list is actually the name of a file,
# but it is declared as phony to force it to be rebuilt every time.
.PHONY: .params-list
.params-list:
aws ssm get-parameters-by-path --path /${SERVICE}/${ENV} | jq -c -r '.Parameters[] | .Name' > $#
.PHONY: params-get
params-get: .params-list
#for param in $$(cat .params-list); do \
aws ssm get-parameter --name $${param} --with-decryption | jq -c -r .Parameter.Value; \
done;