title: What do the -n and -a options do in a bash if statement?
body: <p>What function do the <code>-a</code> and <code>-n</code> options perform in the following bash <code>if</code> statement?</p>
  
  <pre><code>if [ -n "$1" -a -n "$2" -a -n "$3" ]; then
      REFNAME=$(basename $3)
  else
  </code></pre>
  
  <p>Are <code>-a</code> and <code>-n</code> so called <em><a href="http://www.gnu.org/software/bash/manual/html_node/Bash-Conditional-Expressions.html">primaries</a></em>?</p>
  
  <p>Does <code>-a file</code> mean "True if file exists."?</p>