title: write a shell script to add job to cron
body: <p>I write a shell script below to add a job to cron.</p>
  
  <pre><code>#!/bin/sh
  touch date.cron
  echo '*/3 * * * * /usr/sbin/ntpdate 192.168.2.3' &gt;date.cron
  crontab date.cron
  rm date.cron
  </code></pre>
  
  <p>But I don't want to create the file date.cron. How can I add the job directly without creating the file. Any suggestions?</p>