wget

wget 下载不产生文件（crontab定时任务时可能不希望产生文件）

wget -O /dev/null -o /dev/null example.com

Here -O sends the downloaded file to /dev/null and -o logs to /dev/null instead of stderr. That way redirection is not needed at all.

http://serverfault.com/questions/619542/piping-wget-output-to-dev-null-in-cron

命令详解：
http://man.linuxde.net/wget