title: Using `find -perm` to find when a permission is not set
body: <p>I want to find the non-readable files in my directory (eg the files with g-r).  So I tried this:</p>
  
  <p><code>find . -perm -g-r</code></p>
  
  <p>It shows me all of the files??  So I tried this:</p>
  
  <p><code>find . -perm -g+r</code></p>
  
  <p>And it showed me only the readable files.  It appears that <code>-perm -g-r</code> matches all files.  I'm using CentOS 5.5.  Am I doing something wrong?  It doesn't look like <code>-perm -g-r</code> does anything useful.</p>