gnu make - Using variables in Makefile -

gnu make - Using variables in Makefile -

here simple makefile.

filename=test.`date +"%y.%m.%d %h:%m:%s"`.txt test: @echo ${filename} @sleep 2s @echo ${filename}

the output of make test

test.2013.02.18 15:30:23.txt test.2013.02.18 15:30:25.txt

the problem filename beingness calculated each time used. want calculated 1 time , same while script running. doing wrong?

gnu create has 2 flavours of variables. have used recursively-expanded variable, want simply-expanded variable. see http://www.gnu.org/software/make/manual/html_node/flavors.html#flavors

with current makefile, variable contains exact text test.date +"%y.%m.%d %h:%m:%s".txt , every time reference text gets substituted verbatim, , makefile equivalent to:

test: @echo test.`date +"%y.%m.%d %h:%m:%s"`.txt @sleep 2s @echo test.`date +"%y.%m.%d %h:%m:%s"`.txt

seen should obvious shell runs date command twice.

to behaviour want, need set simply-expanded variable , need run shell command @ point define it, can't utilize backticks because shell metacharacters create ignores them, utilize make's shell function instead:

filename := test.$(shell date +"%y.%m.%d %h:%m:%s").txt

makefile gnu-make