• package_version := $(version)x0d$(date)

  what is the x0d part between version and date vars? is it just string?

• What $(dotin_files:.in=) does below

code

dotin_files       := $(shell find . -type f -name \*.in)
dotin_files       := $(dotin_files:.in=)

• what this means $(dotin_files:=.in)

code

$(dotin_files): $(dotin_files:=.in)
 $(substitute) [email protected] > $@

• can target contain multiple files?

• what is the meaning of declaring target variable as PHONY?

code

.PHONY: $(dotin_files)

• In the regex replacement code below

code

substitute := perl -p -e 's/@([^@]+)@/defined $$ENV{$$1} ? $$ENV{$$1} : $$&/ge'

what are $$ENV{$$1} and $$&? I guess it's Perl scope...

thanks for your time