title: What does '-d' do in Unix?
body: <p>I have this code, it was set as a condition for a step.
  what does the '-d' in the code mean?</p>
  
  <pre><code>if [ -d $FTBASEDIR/$1/$2 ]; then
      ftcmd="lcd $FTBASEDIR"
      ftcmd2="cd $FTROOTDIR"
      ftcmd3="put $1"
  fi
  </code></pre>