CODEWITHSUNDEEP
makefile
CSJ
CSJ

Reputation: 2957

Expanded variable values in Makefile

I am learning some basics of Makefile, and write simple example as below:

urname=Chang
givenname=SJ
fullname=$(givenname) $(surname)
hello:
    @echo $(fullname)

surname=Lin

ALL_PACKAGES=
hello1:
ifeq (,$(ALL_PACKAGES))
    @echo There is no package
    $(error $(ALL_PACKAGES) is empty)
else
    @echo there are some packages
endif
    @echo $(ALL_PACKAGES)

ALL_PACKAGES += package1

I can understand make hello result will be "SJ Lin", cause $(surname) is "Lin" finally.

However, in result of make hello1,why $(ALL_PACKAGES) is empty in the if condition(I guess if will be "package1" in the same way on make hello)?

Moreover, why the first echo message("There is no package") will not be printed but only error message do?

Thanks teachers.

Upvotes: 0

Views: 43

Answers (1)

Carl Norum
Carl Norum

Reputation: 224944

  1. make hello will yield "Jay Lin", not "SJ Lin". I don't know where you got "SJ" from.

  2. ALL_PACKAGES is empty at that point in the parsing, so that's why you get that result. The ifeq is handled at the time of parsing the makefile, before it actually starts to run and build targets.

  3. The error message prints out (and causes make to exit) while it is parsing the makefile, before it starts to run and build targets.

  4. If you were to comment out the $(error line, you'll get two printouts from make hello1 - both the There is no package message (included because of the state of ALL_PACKAGES at that point in the parsing), and then also package1, from $(ALL_PACKAGES) being expanded later, during the actual make processing.

Upvotes: 1

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