Lazy Set
VARIABLE = value
Normal setting of a variable, but any other variables mentioned with the value field are recursively expanded with their value at the point at which the variable is used, not the one it had when it was declared
Immediate Set
VARIABLE := value
Setting of a variable with simple expansion of the values inside - values within it are expanded at declaration time.
Lazy Set If Absent
VARIABLE ?= value
Setting of a variable only if it doesn't have a value. value is always evaluated when VARIABLE is accessed. It is equivalent to
ifeq ($(origin VARIABLE), undefined)
VARIABLE = value
endif
See the documentation for more details.
Append
VARIABLE += value
Appending the supplied value to the existing value (or setting to that value if the variable didn't exist)
By default, Makefile targets are "file targets" - they are used to build files from other files. Make assumes its target is a file, and this makes writing Makefiles relatively easy:
foo: bar
create_one_from_the_other foo bar
However, sometimes you want your Makefile to run commands that do not represent physical files in the file system. Good examples for this are the common targets "clean" and "all". Chances are this isn't the case, but you may potentially have a file named clean in your main directory. In such a case Make will be confused because by default the clean target would be associated with this file and Make will only run it when the file doesn't appear to be up-to-date with regards to its dependencies.
These special targets are called phony and you can explicitly tell Make they're not associated with files, e.g.:
.PHONY: clean
clean:
rm -rf *.o
Now make clean will run as expected even if you do have a file named clean.
In terms of Make, a phony target is simply a target that is always out-of-date, so whenever you ask make <phony_target>, it will run, independent from the state of the file system. Some common make targets that are often phony are: all, install, clean, distclean, TAGS, info, check.
Best Answer
G'day,
You need tabs to indent the lines underneath each target.
BTW General convention is that you should use braces rather than brackets for your macros. Using brackets are a legacy thing left over from substituting an object back in to an archive. So the above is better expressed as:
HTH