title: Short/long options with option argument - is this some sort of convention?
body: <p>It seems that most (a lot of) commands implement option arguments like this:</p>
  
  <ol>
  <li><p>if a short option requires an option argument, the option is separated by a space from the option argument, e.g.</p>
  
  <pre><code>$ head -n 10
  </code></pre></li>
  <li><p>if a long option requires an option argument, the option is separated by a <code>=</code> from the option argument, e.g.</p>
  
  <pre><code>$ head --lines=10
  </code></pre></li>
  </ol>
  
  <p>Is this some sort of convention and yes, where can I find it? Besides, what's the reasoning?</p>
  
  <p>Why e.g. is it not</p>
  
  <pre><code>    $ head --lines 10
  </code></pre>
  
  <p>?</p>