title: Minify multiple input file with postcss
body: <p>I installed cssnano following these step: <a href="http://cssnano.co/guides/getting-started/" rel="nofollow noreferrer">http://cssnano.co/guides/getting-started/</a></p>
  
  <p>Into the root of my project i ran:</p>
  
  <pre><code>npm install cssnano --save-dev
  </code></pre>
  
  <p>After i installed postcss-cli:</p>
  
  <pre><code>npm install postcss-cli --global
  </code></pre>
  
  <p>Finally i created postcss.config.js file following the guide:</p>
  
  <pre><code>module.exports = {
     plugins: [
      require('cssnano')({
          preset: 'default',
      }),
    ],
  };
  </code></pre>
  
  <p>I was able to minify only a file. In the roow of my project i executed:</p>
  
  <pre><code>postcss src/plugins/bootstrap/css/bootstrap.css &gt; src/compiled.min.css
  </code></pre>
  
  <p>But i'm not able to include multiple input file (and i don't know if it's possible) as i did in gulp. When i try to run a command of this type:</p>
  
  <pre><code>postcss src/plugins/bootstrap/css/bootstrap.css src/plugins/animatecss/css/animate.css &gt; src/compiled.min.css
  </code></pre>
  
  <p>There was the following error:</p>
  
  <pre><code>Input Error: Must use --dir or --replace with multiple input files
  </code></pre>