title: Bash: what does "-eq" mean?
body: <p>I would like to know what <code>-eq</code> does in a bash script (as in the below example):</p>
  
  <pre><code>LINES=`ps -p $PID`
      PIDRET=$?
      if [ $PIDRET -eq 0 ];
      then
          export PID
          return 0;
      fi
      rm -f "$CATALINA_PID" 
  </code></pre>