build: improve build efficiency

.gitignore

@@ -1,2 +1,5 @@
 *.o
+*.ro
+*.do
+ddish
 dish

Makefile

@@ -1,22 +1,32 @@
-OBJ=main.o line.o loop.o exec.o builtin.o
-CC=gcc
-CFLAGS= -O3 -Wall
+SHELL := /bin/bash
+CC     = gcc
+SRC = main.c loop.c exec.c line.c builtin.c
+OBJ = $(SRC:.c=.ro)
+DBGOBJ = $(SRC:.c=.do)
+EXE  = dish
+DBGEXE = ddish
 
-all:release
-r:release
-release:dish
+all:release debug
+debug: CFLAGS = -g -O0 -DDEBUG
+release: CFLAGS = -Wall -O3
 
-dish: $(OBJ)
-	$(CC) $(CFLAGS) -o dish $(OBJ)
+release: $(OBJ)
+	$(CC) $(CFLAGS) -o $(EXE) $(OBJ)
 
-d: 
-	make clean
-	make debug
+debug: $(DBGOBJ)
+	$(CC) $(CFLAGS) -o $(DBGEXE) $(DBGOBJ)
 
-debug: CFLAGS += -DDEBUG -g
-debug: dish
-
-c: clean
 clean:
-	rm -f $(OBJ) dish
+	rm -f *.o
 
+$(OBJ):$(SRC)
+	$(CC) $(CFLAGS) -c $(SRC)
+	rename .o .ro *.o
+
+$(DBGOBJ):$(SRC)
+	$(CC) $(CFLAGS) -c $(SRC)
+	rename .o .do *.o
+	
+c:clean
+d:debug
+r:release