Makefile rule to build with same name, but different directory

Question

I would like a rule something like:

build/%.ext: src/%.ext
    action

I have one directory of files in a folder that I want to optimize and then output to a different folder. However, the files have the same name in the input and output folders. I have tried various iterations of the rule above, but make will either always or never rebuild depending how I tweak the above. Suggestions?

EDIT: I ended up with the following solution, which works great!

JS = \
  src/js/script2.js \
  src/js/script1.js

JS_OPT = $(patsubst src/js/%.js,web/js/%.js, $(JS))

all: $(JS_OPT)

$(JS_OPT): web/js/%.js: src/js/%.js
  cat $@ | ./bin/jsmin > $<

Answer 1

Try somethink like this:

INPUT_FILES = \
  src/a.txt   \
  src/b.txt   \

OPTIMIZED_FILES=$(patsubst src/%.ext,build/%.ext,$(INPUT_FILES))

$(OPTIMIZED_FILES): build/%.ext: src/%.txt
     optimize_command $@ $<