propagating variables from GNU Make to files

## how do I propagate variables from GNU Make to files?..

## 1st version
## this is totally WRONG solution and given here just for your knowledge

FILES_TEMPLATED :=$(patsubst %.in,%,$(wildcard debian/*.in))
$(FILES_TEMPLATED): %: %.in
    @cp -f $(<) $(@)

.PHONY: process_templates
process_templates: $(FILES_TEMPLATED)
    $(foreach var,$(.VARIABLES),echo -n '$(var)' | grep -Eqe '^[a-zA-Z_][a-zA-Z0-9_]*$$' && grep -Fqe '%$(var)%' $(FILES_TEMPLATED) && sed -re 's/%$(var)%/$($(var))/g' -i $(FILES_TEMPLATED);)

## 2nd version

X :=$(shell printf '\027')

FILES_TEMPLATED :=$(patsubst %.in,%,$(wildcard debian/*.in))

.PHONY: push_templates
push_templates:
    @$(foreach f,$(FILES_TEMPLATED),cp -f '$(f).in' '$(f)';)

.PHONY: process_templates
process_templates: push_templates
    @$(foreach var,$(.VARIABLES),$(if $(shell echo -n '$(var)' | grep -Eqe '^[a-zA-Z_][a-zA-Z0-9_]*$$' && echo ok || true),$(if $(shell grep -Fqe '%$(var)%' $(FILES_TEMPLATED) && echo ok || true),sed -re 's$(X)%$(var)%$(X)$($(var))$(X)g' -i $(FILES_TEMPLATED);)))