Trouble implementing chained variables in Makefile - bash

Question

I'm looking to use the previous variable to look up the next variable (these should all be set as envvars) I have this working in a smaller extent with just profile, but when i try chaining variables together they fall flat...
Expected output is that make build has TF_VARS_* set as envvars and that they are able to be used as regular variables for the next variable input. I assume that there should be an export of TF_VAR_aws_profile TF_VAR_aws_vpc and TF_VAR_aws_net into global scope, this seemed to work fine for when I was JUST using TF_VAR_aws_profile and was able to confirm with echo $TF_VAR_aws_profile
export TF_VAR_aws_profile TF_VAR_aws_vpc TF_VAR_aws_net
# An implicit guard target, used by other targets to ensure
# that environment variables are set before beginning tasks
assert-%:
# if [ "${${*}}" = "" ] ; then \
echo "Environment variable $* not set" ; \
exit 1 ; \
fi
vault:
## This is the problem section here....
# read -p "Enter AWS Profile Name: " profile ; \
vpc=$(shell aws --profile "$${profile}" --region us-west-2 ec2 describe-vpcs |jq -r '.[] | first | .VpcId') ; \
net=$(shell aws --profile "$${profile}" --region us-west-2 ec2 describe-subnets --filters "Name=vpc-id,Values=$${vpc}" |jq -r '.[] | first | .SubnetId') ; \
TF_VAR_aws_profile=$$profile TF_VAR_aws_vpc=$$vpc TF_VAR_aws_net=$$net make build && \
TF_VAR_aws_profile=$$profile make keypair && \
TF_VAR_aws_profile=$$profile make plan && \
TF_VAR_aws_profile=$$profile make apply
build: require-packer
aws-vault exec $(TF_VAR_aws_profile) --assume-role-ttl=60m -- \
"/usr/local/bin/packer" "build" \
"-var" "builder_subnet_id=$(TF_VAR_aws_net)" \
"-var" "builder_vpc_id=$(TF_VAR_aws_vpc)" \
"packer/vault.json"
require-packer: assert-TF_VAR_aws_vpc assert-TF_VAR_aws_net
# echo "[info] VPC: $(TF_VAR_aws_vpc)" ## Not set
# echo "[info] NET: $(TF_VAR_aws_net)" ## Not set
packer --version &> /dev/null
UPDATE
Looks like it might be something to do with line termination on the vault expression, added ; \ to continue the lines

Answer 1

Got it, it was a combination of TWO things, one running as $(shell \$CMD) does not evaluate the inner expression variables, I needed to revert to ticks instead to evaluate variables (keep in mind, variables STILL need $$ in order to evaluate inside of Makefiles) as well as the lines needed to be continued, so terminating only with ; is not effective, we need to use ; \.
Please note that I updated my variable names from above, they are now $$subnet and $$prvnet because I'm a spacing nazi...
export TF_VAR_aws_profile TF_VAR_aws_prvnet TF_VAR_aws_subnet
# An implicit guard target, used by other targets to ensure
# that environment variables are set before beginning tasks
assert-%:
# if [ "${${*}}" = "" ] ; then \
echo "Environment variable $* not set" ; \
exit 1 ; \
fi
vault:
# read -p "Enter AWS Profile Name: " profile ; \
prvnet=`aws --profile "$${profile}" --region us-west-2 ec2 describe-vpcs |jq -r '.[] | first | .VpcId'` ; \
subnet=`aws --profile "$${profile}" --region us-west-2 ec2 describe-subnets --filters "Name=vpc-id,Values=$${prvnet}" |jq -r '.[] | first | .SubnetId'` ; \
TF_VAR_aws_profile=$$profile TF_VAR_aws_prvnet=$$prvnet TF_VAR_aws_subnet=$$subnet make build && \
TF_VAR_aws_profile=$$profile make keypair && \
TF_VAR_aws_profile=$$profile make plan && \
TF_VAR_aws_profile=$$profile make apply
build: require-packer
aws-vault exec $(TF_VAR_aws_profile) --assume-role-ttl=60m -- \
"/usr/local/bin/packer" "build" \
"-var" "builder_subnet_id=$(TF_VAR_aws_net)" \
"-var" "builder_vpc_id=$(TF_VAR_aws_vpc)" \
"packer/vault.json"
require-packer: assert-TF_VAR_aws_prvnet assert-TF_VAR_aws_subnet
# echo "[info] VPC: $(TF_VAR_aws_prvnet)" ;
# echo "[info] NET: $(TF_VAR_aws_subnet)" ;
packer --version &> /dev/null