Makefile Variables Example

Make-File Instruction for Variables

If we use the GNU, then we should add one line to the make-file before debugging. It is so useful that we should do it all the time and in every make-file that we create.

print-%: ; @echo $*=$($*)

This line allows us to quickly get the value of any variable in the make-file. For example, if we want to know the value of a variable with the name “SOURCE_FILES” then we just need to enter: make print-SOURCE_FILES. If we are using GNU Make 3.82 or higher, we do not even need to change the assembly itself and enter the following:

make --eval="print-%: ; @echo $*=$($*)" print-SOURCE_FILES

So we get the value of SOURCE_FILES. The “–eval” adds the make-file to our string without changing it, which is a very convenient way if it is necessary to keep the assembly intact.

How does this work?

String

print-%: ; @echo $*=$($*)
This defines a template on which instead of the sign “%” may be the sought variable. So when we ask for a printout of the SOURCE_FILES to, then this rule will be fulfilled, as % will be is implied by our variable of SOURCE_FILES. The @echo $ * = $ ($ *) command is a command that runs under the command print-%. A semicolon is used to separate the two commands from each other and eliminates the need to write it in two rows. However, it looks like this in a more traditional way:


print-%:
@echo $*=$($*)

As we can see, the use of semicolons slightly simplifies everything. The automatic variable $* corresponds to %  in the print-% (when we run “print-SOURCE_FILES” our variable $* will correspond to SOURCE_FILES). Thus, $* contains the name of the variable that we want to output. And $($ *) is the value of the variable whose name is stored in $*. For example, $* gets the name of the SOURCE_FILES, and GNU Make gets the value stored in $(SOURCE_FILES). Saving the content of one variable to another variable can be a very useful method for many make-files.

 

Thanks for your attention!

 

During your programming courses you should learn a lot of useful commands and libraries that will help you to write clear and well-structured code. If you were assigned a task with makefile variables, check our instructions and example of implication written by one of our experts! AssignmentShark has united the best professionals in one team to provide help with programming, beginning with basic functions and moving up to advanced programming assistance.


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