Make Makefile strictly POSIX compliant

Thanks Hiltjo for the feedback! GNUisms need to be avoided like a
plague, even if it means having to be a little more creative.

Strict POSIX compliance means that I just worked within the bounds of
the POSIX specification, hopefully without using any GNU or BSD
extensions. If I did, please let me know.

Tip to all Linux users: Test your Makefiles with pmake(1) instead of
make(1) (= GNU make) and refer to the newest POSIX 2016 make
specification[0].

[0]: http://pubs.opengroup.org/onlinepubs/9699919799/utilities/make.html

2 files changed, 17 insertions, 16 deletions

diff --git a/Makefile b/Makefile
index dcbbeed..5d9c213 100644
--- a/Makefile
+++ b/Makefile
@@ -1,31 +1,32 @@
-# farbfeld - suckless image format with conversion tools
 # See LICENSE file for copyright and license details
+# farbfeld - suckless image format with conversion tools
+.POSIX:
+
 include config.mk
 
-REQ =
 HDR = arg.h
 BIN = png2ff ff2png jpg2ff ff2jpg ff2pam ff2ppm
-SCRIPTS = 2ff
+SCR = 2ff
 MAN1 = 2ff.1 $(BIN:=.1)
 MAN5 = farbfeld.5
 
 all: $(BIN)
 
-$(BIN): % : %.o $(REQ:=.o)
-	$(CC) $^ $(LDFLAGS) -o $@
+.o: $(REQ:=.o)
+	$(CC) $(CFLAGS) $($*-LDFLAGS) -o $@ $< $(REQ:=.o)
 
-$(BIN:=.o): $(HDR) $(REQ:=.h)
-
-%.o: %.c config.mk
+.c.o:
 	$(CC) $(CPPFLAGS) $(CFLAGS) -c $<
 
+$(BIN:=.o): config.mk $(HDR) $(REQ:=.h)
+
 clean:
 	rm -f $(BIN) $(BIN:=.o) $(REQ:=.o)
 
 dist:
 	rm -rf "farbfeld-$(VERSION)"
 	mkdir -p "farbfeld-$(VERSION)"
-	cp -R FORMAT LICENSE Makefile README TODO config.mk $(SCRIPTS) \
+	cp -R FORMAT LICENSE Makefile README TODO config.mk $(SCR) \
 	      $(HDR) $(BIN:=.c) $(REQ:=.c) $(REQ:=.h) \
 	      $(MAN1) $(MAN5) "farbfeld-$(VERSION)"
 	tar -cf - "farbfeld-$(VERSION)" | gzip -c > "farbfeld-$(VERSION).tar.gz"
@@ -33,8 +34,8 @@ dist:
 
 install: all
 	mkdir -p "$(DESTDIR)$(PREFIX)/bin"
-	cp -f $(SCRIPTS) $(BIN) "$(DESTDIR)$(PREFIX)/bin"
-	for f in $(BIN) $(SCRIPTS); do chmod 755 "$(DESTDIR)$(PREFIX)/bin/$$f"; done
+	cp -f $(SCR) $(BIN) "$(DESTDIR)$(PREFIX)/bin"
+	for f in $(BIN) $(SCR); do chmod 755 "$(DESTDIR)$(PREFIX)/bin/$$f"; done
 	mkdir -p "$(DESTDIR)$(MANPREFIX)/man1"
 	cp -f $(MAN1) "$(DESTDIR)$(MANPREFIX)/man1"
 	for m in $(MAN1); do chmod 644 "$(DESTDIR)$(MANPREFIX)/man1/$$m"; done
@@ -43,8 +44,6 @@ install: all
 	for m in $(MAN5); do chmod 644 "$(DESTDIR)$(MANPREFIX)/man5/$$m"; done
 
 uninstall:
-	for f in $(BIN) $(SCRIPTS); do rm -f "$(DESTDIR)$(PREFIX)/bin/$$f"; done
+	for f in $(BIN) $(SCR); do rm -f "$(DESTDIR)$(PREFIX)/bin/$$f"; done
 	for m in $(MAN1); do rm -f "$(DESTDIR)$(MANPREFIX)/man1/$$m"; done
 	for m in $(MAN5); do rm -f "$(DESTDIR)$(MANPREFIX)/man5/$$m"; done
-
-.PHONY: all clean dist install uninstall
diff --git a/config.mk b/config.mk
index 93988c4..d5bc6c7 100644
--- a/config.mk
+++ b/config.mk
@@ -12,8 +12,10 @@ CPPFLAGS = -D_DEFAULT_SOURCE
 CFLAGS   = -std=c89 -pedantic -Wall -Os
 LDFLAGS  = -s
 
-png2ff ff2png: LDFLAGS += -lpng
-jpg2ff ff2jpg: LDFLAGS += -ljpeg
+png2ff-LDFLAGS = -lpng
+ff2png-LDFLAGS = -lpng
+jpg2ff-LDFLAGS = -ljpeg
+ff2jpg-LDFLAGS = -ljpeg
 
 # compiler and linker
 CC = cc