Home / Questions / 4284
Accepted
Gepser Hoil
Asked: 2020-02-17 08:27:27 +0800 CST 2020-02-17 08:27:27 +0800 CST

What does the .PHONY mean in the Makefiles?

  • 772

I have come across this many times: .PHONYat the end of files Makefileand would like to know what it means. I have used Makefilesbut never needed to add that.

A concrete example of what I found now:

.PHONY: \
  all \
  test \
  clean \
  release
makefile

1 Answers

  1. Best Answer

    Translating George Y. 's answer from Stack Overflow to the question What is the purpose of .PHONY in a makefile? . The explanation is simple and quite good.

    Let's assume you have the "install" target, which is very common in makefiles. If you don't use .PHONY, and there is a file called "install" in the same directory as the Makefile, then the command make installwill do nothing. This occurs because Make interprets the rule as "execute this-and-this recipe to create the file named install". Since the file is already there, and the dependencies haven't changed, nothing will happen.

    However, if you make the "install" target a PHONY, you will tell the tool makethat the target is dummy, and that makeit should not create the file. Therefore it will not check that the "install" file exists, which means that:

    1. Its behavior will not be altered if the file actually exists
    2. The stat()extra will not be called

    Generally all targets in your Makefile that do not produce an output file with the same name as the target name should be of type PHONY. This typically includes a all, install, clean, distclean, etc.

    The following example of the answer taken from the same question created by Eli Bendersky should make it clearer.

    These special targets are called PHONY and you can explicitly tell Make that they are not associated with files, for example:

    .PHONY: clean
clean:
  rm -rf *.o
    • 7