--- Makefile.orig	2005-11-02 16:44:21.000000000 +0800
+++ Makefile	2014-06-19 23:50:39.847155161 +0800
@@ -1,7 +1,7 @@
 
-CC = gcc
-CFLAGS = -Wall -O
-DESTDIR = /usr/local
+CC ?= gcc
+CFLAGS += -Wall
+#DESTDIR = ${PREFIX}
 
 loop:
 	${CC} ${CFLAGS} -o loop loop.c
@@ -17,6 +17,6 @@ clean:
 	rm -f loop loop.1.gz
 
 install: loop man
-	install loop ${DESTDIR}/bin
-	install loop.1.gz $(DESTDIR)/man/man1
+	install loop $(DESTDIR)${PREFIX}/bin
+	install loop.1.gz $(DESTDIR)${PREFIX}/man/man1