using ?= operator

Author: Vlad Ionescu

Makefile

@@ -1,19 +1,10 @@
-ifndef TMPDIR
-TMPDIR := /tmp
-endif
 
-ifndef RABBITMQ_NODENAME
-RABBITMQ_NODENAME:=rabbit
-endif
-ifndef RABBITMQ_SERVER_START_ARGS
-RABBITMQ_SERVER_START_ARGS:=
-endif
-ifndef RABBITMQ_MNESIA_DIR
-RABBITMQ_MNESIA_DIR:=$(TMPDIR)/rabbitmq-$(RABBITMQ_NODENAME)-mnesia
-endif
-ifndef RABBITMQ_LOG_BASE
-RABBITMQ_LOG_BASE:=$(TMPDIR)
-endif
+TMPDIR ?= /tmp
+
+RABBITMQ_NODENAME ?= rabbit
+RABBITMQ_SERVER_START_ARGS ?=
+RABBITMQ_MNESIA_DIR ?= $(TMPDIR)/rabbitmq-$(RABBITMQ_NODENAME)-mnesia
+RABBITMQ_LOG_BASE ?= $(TMPDIR)
 
 SOURCE_DIR=src
 EBIN_DIR=ebin