title: work of -z in unix
body: <pre><code>if [ -z "${ABC}" ] 
  then
  LOGDIR=`${JAVA_HOME}/bin/java -cp ${a}/aim.jar my.app.util.GetLogDir "${rsp}"`
  </code></pre>
  
  <p>Can some one help me with this. What this if is exactly doing.
  Is it checking if abc exists and the calling GetLogDir's main with some arguments?</p>