title: Doing parallel processing in bash?
body: <p>I've thousands of png files which I like to make smaller with <code>pngcrush</code>. I've a simple <code>find .. -exec</code> job, but it's sequential. My machine has quite some resources and I'd make this in parallel.</p>
  
  <p>The operation to be performed on every png is:</p>
  
  <pre><code>pngcrush input output &amp;&amp; mv output input
  </code></pre>
  
  <p>Ideally I can specify the maximum number of parallel operations.</p>
  
  <p>Is there a way to do this with bash and/or other shell helpers? I'm Ubuntu or Debian.</p>