Makefile：如何设置一个LOGFILE =`date +'test_％m。％d_％H.％M.％S.log'`变量只有一次？(Makefile: how to set a LOGFILE=`date +'test_%m.%d_%H.%M.%S.log'` variable only once?)

 我喜欢将测试程序的输出记录到带有时间戳的日志文件中。 
 
 我创建了以下Makefile，但它不起作用。 “make”似乎根据需要在最后时刻计算LOGFILE。 
 
 Makefile文件 
 
LOGFILE=`date +'test_%m.%d_%H.%M.%S.log'`
export DLOG=$(LOGFILE)
test2:
    echo DLOG=$$DLOG
    echo DLOG=${DLOG}
    sleep 2
    echo DLOG=${DLOG}
 
 make test2 
 
echo DLOG=$DLOG
DLOG=`date +'test_%m.%d_%H.%M.%S.log'`
echo DLOG=`date +'test_%m.%d_%H.%M.%S.log'`
DLOG=test_10.22_10.28.04.log
sleep 2
echo DLOG=`date +'test_%m.%d_%H.%M.%S.log'`
DLOG=test_10.22_10.28.06.log
 
 我想找到一些“make”只计算一次LOGFILE或DLOG变量，我可以在makefile中的任何地方使用相同的值。 可能吗？ 

I like to log output of test program to a log file with time stamp.
 
I created following Makefile, but it doesn't work. The "make" seems to calculate LOGFILE at the last moment as needed. 
 
Makefile
 
LOGFILE=`date +'test_%m.%d_%H.%M.%S.log'`
export DLOG=$(LOGFILE)
test2:
    echo DLOG=$$DLOG
    echo DLOG=${DLOG}
    sleep 2
    echo DLOG=${DLOG}
 
make test2
 
echo DLOG=$DLOG
DLOG=`date +'test_%m.%d_%H.%M.%S.log'`
echo DLOG=`date +'test_%m.%d_%H.%M.%S.log'`
DLOG=test_10.22_10.28.04.log
sleep 2
echo DLOG=`date +'test_%m.%d_%H.%M.%S.log'`
DLOG=test_10.22_10.28.06.log
 
I like to find someway to have the "make" calculate the LOGFILE or DLOG variable only once and I can use the same value everywhere in the makefile. Is it possible?

原文：https://stackoverflow.com/questions/33287226