title: what does the following "$?run" mean in shell csh
body: <p>What <code>$?run</code> does in the following example? <code>run</code> is variation with <code>run</code> directory. I understand that <code>$?</code> has the status of the last command.  </p>
  
  <pre><code>if ( ! $?run ) then  
    set run = $PWD
  endif
  </code></pre>