Makefile: Expansion of "$<" does not work in "optimized" makefile

Question

I have a directory structure like this:

./
|
|- values-1/
|  |- thing0.yaml
|
|- values-2/
|  |- thing1.yaml
|
|- dachart-1/
|  |- thing0.yaml   (this should be generated by make
|                    from values-1/thing0.yaml)
|- dachart-2/
|  |- thing1.yaml   (this should be generated by make
                     from values-2/thing1.yaml)

the "build rules" are basically identical, but about 30 lines long.

this very simple Makefile illustrates what works:

# WORKING makefile, but with two redundant build rules

.SOURCES:

SHELL=bash

src1_files := $(wildcard values-1/*.yaml)
src2_files := $(wildcard values-2/*.yaml)
dst1_files := $(patsubst values-%,dachart-%,$(src1_files))
dst2_files := $(patsubst values-%,dachart-%,$(src2_files))

all: $(dst2_files) $(dst1_files)

dachart-1/%.yaml: values-1/%.yaml
    # SIMPLIFIED EXAMPLES
    @echo "source $<"
    @echo "target $@"

dachart-2/%.yaml: values-2/%.yaml
    @echo "source $<"
    @echo "target $@"

But since the build rules are really long and exactly the same, I would like to have one build rule definition for all the files.

After some fooling around I came up with a Makefile that seems to do what I want (and does not error out), alas the $< expansion does no longer work (see output below).

# NON-working makefile, but kinda what I want (only one build rule)

dachart-1/%.yaml: $(src1_files)
dachart-2/%.yaml: $(src2_files)

%.yaml:
    @echo "source $<"
    @echo "target $@"

The outputs are:

# working makefile
source values-1/thing0.yaml
target dachart-1/thing0.yaml

# alternate makefile
source
target dachart-1/thing0.yaml

QUESTION: Is there a way to have only one build rule in the sense of my non-working Makefile?

score 0 · Answer 1 · answered Aug 03 '22 at 13:15

okay, surprisingly this works:

.SOURCES:

SHELL=bash

src1_files := $(wildcard values-0.1/*.yaml)
src2_files := $(wildcard values-2.0/*.yaml)
dst1_files := $(patsubst values-%,dachart-%,$(src1_files))
dst2_files := $(patsubst values-%,dachart-%,$(src2_files))

all: $(dst2_files) $(dst1_files)

fresh: clean all
.PHONY: fresh

dachart-0.1/%.yaml: THING=one
dachart-0.1/%.yaml: $(src1_files)

dachart-2.0/%.yaml: THING=two
dachart-2.0/%.yaml: $(src2_files)


dachart-*/%.yaml: values-*/%.yaml
    @echo THING=${THING}
    @echo "source $<"
    @echo "target $@"

Makefile: Expansion of "$<" does not work in "optimized" makefile

1 Answers1