title: NSIS relative directory to absolute
body: <p>In NSIS I need to convert path, that contains relative part to absolute
  without <strong>"..\"</strong> or <strong>"../"</strong> .
  For example:</p>
  
  <pre><code>StrCpy $0 "C:\Windows\System"
  StrCpy $1 "$0\..\"
  </code></pre>
  
  <p>I need some function to return <strong>"C:\Windows"</strong> in this case</p>