This is a crosspost from my TIL

What the heck is .PHONY in makefile? I have seen this for so long but I always shrugged off. Whatever that is. Well, finally I decided to learn about it.

A bit of introduction to Makefile syntax.

target: prerequisites
<TAB> recipe

The first target in a Makefile will be executed by default when we call make.

blah: blah.o
    cc blah.o -o blah # Runs third

blah.o: blah.c
    cc -c blah.c -o blah.o # Runs second

blah.c:
    echo "int main() { return 0; }" > blah.c # Runs first

In the above example, blah, blah.o and blah.c are targets and they are all files.

Then I created a Makefile

viggy28@localhost:~$ cat Makefile
date:
	date
hostname:
	hostname
hostnameee:
	hostnameee	

If you have a file named as the target already in your filesystem, then make target doesn’t work.

Example. date is a target, however I have touched a file called date.

viggy28@localhost:~$ touch date

viggy28@localhost:~$ make date
make: 'date' is up to date.

viggy28@localhost:~$ rm date

viggy28@localhost:~$ make date
date
Thu Apr 15 23:28:01 UTC 2021

So, how can I avoid that? Enter .PHONY. If you are not targeting a file then change that target to .PHONY

Let’s continue the same example:

viggy28@localhost:~$ cat Makefile
.PHONY: date
date:
	date
hostname:
	hostname
hostnameee:
	hostnameee

I have made target date as a phony target.

viggy28@localhost:~$ ls -lrth date
-rw-r--r-- 1 viggy28 viggy28 0 Apr 15 23:51 date

viggy28@localhost:~$ make date
date
Thu Apr 15 23:28:01 UTC 2021

Even though the file named date does exist, still the target date does work. That answers what .PHONY does.

• make
• linux