title: Why does following makefile rebuilt target "build" everytime
body: <p>I have the following code to untar all the files in a directory and move it to build directory. If I call make multiple times, it tries to execute "build" target everytime even if build directory already exists. Has anyone comes across this? </p>
  
  <p>I found this question but it is not the same.
  <a href="https://stackoverflow.com/questions/8289026/makefile-always-running-target">Makefile always running target</a></p>
  
  <p>OS: Ubuntu 12.04
  Program: GNU Make 3.81</p>
  
  <pre><code>build: mkBuildDir untar 
      chmod 700 build
  
  .PHONY: mkBuildDir untar 
  
  mkBuildDir: 
      mkdir build 
  
  untar: *.tar.gz
      for prefix in *.tar.gz; do \
          tar xvf $$prefix --directory=build; \
      done
  
  clean: 
      rm -Rf build
  </code></pre>