Ubuntu 下关于crontab的使用详解

小鱼儿 2022-08-14 03:44 347阅读 0赞

如果碰到了需要在指定的时间运行php脚本的情况，比如定时进行网站的数据统计、自动执行数据库备份任务、定时发送email等等。

如果我们不使用Cron来执行php脚本，或许我们会采用php include的方法。

比如在index.php 中添加代码：<?php include "crontab.php"?>

当访客通过浏览器访问http://xxxx/index.php的时候，自动执行了crontab.php。

当然这只是一种思路，这种方法并不能指定时间定时运行PHP脚本，同时也给index.php带来了额外的服务器消耗。而Linux Ubuntu Crontab 可以很好地完成php 定时任务

CGI 模块

如果Server API是cgi，那么在需要cron执行的php脚本的第一行额外加入一段代码

\#!/usr/bin/php -q（类似PERL语法），指定服务器中php可执行程序的位置

具体步骤如下：

1.  确认Ubuntu系统已经安装了php5-cli模块安装命令：apt-get install php5-cli。在目录 /usr/bin/php下生成 php可执行程序。

2.  编辑待定时执行的php脚本文件crontab.php，如:

<table style="padding:0px; margin:0px auto 10px; font-size:12px; border-collapse:collapse"> 
 <tbody style="padding:0px!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:inherit!important"> 
  <tr style="padding:0px!important; margin:0px!important; font-size:1em!important; border:0px!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; min-height:inherit!important"> 
   <td style="padding:0px!important; margin:0px!important; font-size:1em!important; border:0px!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:inherit!important; color:rgb(175,175,175)!important"> 
    <div style="word-wrap:normal; padding:0px 0.5em 0px 1em!important; margin:0px!important; border-width:0px 3px 0px 0px!important; border-right-style:solid!important; border-right-color:rgb(108,226,108)!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:right!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:inherit!important; white-space:pre!important">
      1 
    </div> 
    <div style="word-wrap:normal; padding:0px 0.5em 0px 1em!important; margin:0px!important; border-width:0px 3px 0px 0px!important; border-right-style:solid!important; border-right-color:rgb(108,226,108)!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:right!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:inherit!important; white-space:pre!important">
      2 
    </div> 
    <div style="word-wrap:normal; padding:0px 0.5em 0px 1em!important; margin:0px!important; border-width:0px 3px 0px 0px!important; border-right-style:solid!important; border-right-color:rgb(108,226,108)!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:right!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:inherit!important; white-space:pre!important">
      3 
    </div> 
    <div style="word-wrap:normal; padding:0px 0.5em 0px 1em!important; margin:0px!important; border-width:0px 3px 0px 0px!important; border-right-style:solid!important; border-right-color:rgb(108,226,108)!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:right!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:inherit!important; white-space:pre!important">
      4 
    </div> </td> 
   <td style="height:26px; width:692px; padding:0px!important; margin:0px!important; font-size:1em!important; line-height:1.1em!important; float:none!important; border:0px!important; bottom:auto!important; left:auto!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:inherit!important"> 
    <div style="padding:0px!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:relative!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:inherit!important"> 
     <div style="white-space:nowrap; padding:0px 1em!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:inherit!important"> 
      <code style="padding:0px!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important">#!/usr/bin/php&nbsp;-q</code> 
     </div> 
     <div style="white-space:nowrap; padding:0px 1em!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:inherit!important"> 
      <code style="padding:0px!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important">&lt;?php</code> 
     </div> 
     <div style="white-space:nowrap; padding:0px 1em!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:inherit!important"> 
      <code style="padding:0px!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important">&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="padding:0px!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important; color:rgb(170,119,0)!important">$file</code>&nbsp; 
      <code style="padding:0px!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important">=&nbsp;</code> 
      <code style="padding:0px!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important; color:blue!important">"/var/www/"</code> 
      <code style="padding:0px!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important">.</code> 
      <code style="padding:0px!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important; color:rgb(255,20,147)!important">date</code> 
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      <code style="padding:0px!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important">).</code> 
      <code style="padding:0px!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important; color:blue!important">'_'</code> 
      <code style="padding:0px!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important">.</code> 
      <code style="padding:0px!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important; color:rgb(255,20,147)!important">date</code> 
      <code style="padding:0px!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important">(</code> 
      <code style="padding:0px!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important; color:blue!important">'i'</code> 
      <code style="padding:0px!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important">).</code> 
      <code style="padding:0px!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important; color:blue!important">'_'</code> 
      <code style="padding:0px!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important">.</code> 
      <code style="padding:0px!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important; color:rgb(255,20,147)!important">date</code> 
      <code style="padding:0px!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important">(</code> 
      <code style="padding:0px!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important; color:blue!important">'s'</code> 
      <code style="padding:0px!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important">).</code> 
      <code style="padding:0px!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important; color:blue!important">'.txt'</code> 
      <code style="padding:0px!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important">;</code> 
     </div> 
     <div style="white-space:nowrap; padding:0px 1em!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:inherit!important"> 
      <code style="padding:0px!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important">&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="padding:0px!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important; color:rgb(255,20,147)!important">file_put_contents</code> 
      <code style="padding:0px!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important">(</code> 
      <code style="padding:0px!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important; color:rgb(170,119,0)!important">$file</code> 
      <code style="padding:0px!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important">,</code> 
      <code style="padding:0px!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important; color:rgb(255,20,147)!important">date</code> 
      <code style="padding:0px!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important">(</code> 
      <code style="padding:0px!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important; color:blue!important">'Y-m-d'</code> 
      <code style="padding:0px!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important">));</code> 
     </div> 
    </div> </td> 
  </tr> 
 </tbody> 
</table>

3.  编辑 crontab 任务：

打开终端，输入命令：crontab -e，

Select an editor.  To change later, run 'select-editor'.

1. /bin/ed

2. /bin/nano        <---- easiest

3. /usr/bin/vim.tiny

选择一个Ubuntu编辑器后，编辑/tmp/crontab.AuN7IQ/crontab 文件：

\# m h  dom mon dow   command

在下面添加定时执行命令：

\* \* \* \* \* php /path/to/your/cron.php

5个星号分别代表定时指定每分、小时、日、月、周。如每天的下午7点执行crontab.php，命令为：

\* 19 \* \* \* php /var/www/cron/crontab.php

然后按Ctrl+O保存，Ctrl+X退出。

Apache 模块

如果php安装是以 apache 模式运行的，那么在要在ubuntu服务器定时执行的php脚本开头就不用加\#!/usr/bin/php  -q 这一行。php脚本在ubuntu 通过crontab的定时执行通过Lynx浏览器的自动访问来完成。

1.  Lynx浏览器安装。

Lynx浏览器是一款轻便的web浏览器，使用于大部分Unix 和Linux系统环境。

安装命令：sudo apt-get install lynx

2. 编辑cron任务，命令crontab -e

\* \* \* \* \* lynx -dump http://xxxx.com/cron.php

注意这个地址最好用绝对地址，包含“http://”的完整url。

通过CURL来完成远程调用

1、创建计划任务,使用crontab命令:

crontab -e

执行这条命令，选择计划任务编辑器，一般选择nano(比较简单)

2、输入要执行的PHP代码或者其他URL的网页:

\*/3 \* \* \* \* /usr/bin/curl -o temp.txt http://localhost/monitor.php

上面这条命令的意思是每隔三分钟执行一次monitor.php这个代码文件，从坐到右依次是分、时、天、月、年，也可以指定在某段时间内执行：

\*/3 9-18 \* \* \* /usr/bin/curl -o temp.txt http://localhost/monitor.php

即在早上9点到晚上6点，每隔三分钟执行依次monitor.php代码。

3、输入以上命令后按Ctrl+X,并选择Yes，保存计划任务，这样就成功创建了一个crontab,要查看当前用户的计划任务列表，输入一下命令：

crontab -l

crontab知识普及

使用crontab定时执行php代码，例如：每隔十分钟执行一次：  
/10 \* \* \* \* wget -q --sqider http://\*\*\*\*\*\*  
一、在Crontab中使用PHP执行脚本   
就像在Crontab中调用普通的shell脚本一样（具体Crontab用法），使用PHP程序来调用PHP脚本。   
每一小时执行myscript.php如下：

代码如下:

\# crontab -e   
00 \* \* \* \* /usr/local/bin/php /home/john/myscript.php

/usr/local/bin/php为PHP程序的路径。   
二、在Crontab中使用URL执行脚本   
如果你的PHP脚本可以通过URL触发，你可以使用lynx或curl或wget来配置你的Crontab。   
下面的例子是使用Lynx文本浏览器访问URL来每小时执行PHP脚本。Lynx文本浏览器默认使用对话方式打开URL。但是，像下面的，我们在lynx命令行中使用-dump选项来把URL的输出转换来标准输出。

代码如下:

00 \* \* \* \* lynx -dump http://www./myscript.php

下面的例子是使用CURL访问URL来每5分执行PHP脚本。Curl默认在标准输出显示输出。使用”curl -o”选项，你也可以把脚本的输出转储到临时文件。

代码如下:

\*/5 \* \* \* \* /usr/bin/curl -o temp.txt http://www./myscript.php

下面的例子是使用WGET访问URL来每10分执行PHP脚本。-q选项表示安静模式。”-O temp.txt”表示输出会发送到临时文件。

代码如下:

\*/10 \* \* \* \* /usr/bin/wget -q -O temp.txt http://www./myscript.php

下面对他做一个详细的介绍：  
名称 : crontab   
使用权限 : 所有使用者   
使用方式 :   
crontab \[ -u user \] file   
crontab \[ -u user \] \{ -l | -r | -e \}   
说明 :   
crontab 是用来让使用者在固定时间或固定间隔执行程序之用，换句话说，也就是类似使用者的时程表。-u user 是指设定指定 user 的时程表，这个前提是你必须要有其权限(比如说是 root)才能够指定他人的时程表。如果不使用 -u user 的话，就是表示设定自己的时程表。   
参数 :   
crontab -e : 执行文字编辑器来设定时程表，内定的文字编辑器是 VI，如果你想用别的文字编辑器，则请先设定 VISUAL 环境变数来指定使用那个文字编辑器(比如说 setenv VISUAL joe)   
crontab -r : 删除目前的时程表   
crontab -l : 列出目前的时程表   
crontab file \[-u user\]-用指定的文件替代目前的crontab。  
时程表的格式如下 :   
f1 f2 f3 f4 f5 program   
其中 f1 是表示分钟，f2 表示小时，f3 表示一个月份中的第几日，f4 表示月份，f5 表示一个星期中的第几天。program 表示要执行的程序。   
当 f1 为 \* 时表示每分钟都要执行 program，f2 为 \* 时表示每小时都要执行程序，其馀类推   
当 f1 为 a-b 时表示从第 a 分钟到第 b 分钟这段时间内要执行，f2 为 a-b 时表示从第 a 到第 b 小时都要执行，其馀类推   
当 f1 为 \*/n 时表示每 n 分钟个时间间隔执行一次，f2 为 \*/n 表示每 n 小时个时间间隔执行一次，其馀类推   
当 f1 为 a, b, c,... 时表示第 a, b, c,... 分钟要执行，f2 为 a, b, c,... 时表示第 a, b, c...个小时要执行，其馀类推   
使用者也可以将所有的设定先存放在档案 file 中，用 crontab file 的方式来设定时程表。  
例子 :   
\#每天早上7点执行一次 /bin/ls :   
0 7 \* \* \* /bin/ls   
在 12 月内, 每天的早上 6 点到 12 点中，每隔3个小时执行一次 /usr/bin/backup :   
0 6-12/3 \* 12 \* /usr/bin/backup   
周一到周五每天下午 5:00 寄一封信给 alex@domain.name :   
0 17 \* \* 1-5 mail -s "hi" alex@domain.name < /tmp/maildata   
每月每天的午夜 0 点 20 分, 2 点 20 分, 4 点 20 分....执行 echo "haha"   
20 0-23/2 \* \* \* echo "haha"   
注意 :   
当程序在你所指定的时间执行后，系统会寄一封信给你，显示该程序执行的内容，若是你不希望收到这样的信，请在每一行空一格之后加上 > /dev/null 2>&1 即可  
例子2 :  
\#每天早上6点10分   
10 6 \* \* \* date   
\#每两个小时   
0 \*/2 \* \* \* date   
\#晚上11点到早上8点之间每两个小时，早上8点   
0 23-7/2，8 \* \* \* date   
\#每个月的4号和每个礼拜的礼拜一到礼拜三的早上11点   
0 11 4 \* mon-wed date   
\#1月份日早上4点   
0 4 1 jan \* date   
范例   
$crontab -l 列出用户目前的crontab.  
 crontab命令的功能是在一定的时间间隔调度一些命令的执行。在/etc目录下有一个crontab文件，这里存放有系统运行的一些调度程序。每个用户可以建立自己的调度crontab。   
crontab命令有三种形式的命令行结构：   
crontab \[-u user\] \[file\]   
crontab \[-u user\] \[-e|-l|-r\]   
crontab -l -u \[-e|-l|-r\] 第一个命令行中，file是命令文件的名字。如果在命令行中指定了这个文件，那么执行crontab命令，则将这个文件拷贝到crontabs目录下；如果在命令行中没有制定这个文件，crontab命令将接受标准输入（键盘）上键入的命令，并将他们也存放在crontab目录下。   
  
命令行中-r选项的作用是从/usr/spool/cron/crontabs目录下删除用户定义的文件crontab；   
命令行中-l选项的作用是显示用户crontab文件的内容。   
使用命令crontab -u user -e命令编辑用户user的cron(c)作业。用户通过编辑文件来增加或修改任何作业请求。   
  
执行命令crontab -u user -r即可删除当前用户的所有的cron作业。   
作业与它们预定的时间储存在文件/usr/spool/cron/crontabs/username里。username使用户名，在相应的文件中存放着该用户所要运行的命令。命令执行的结果，无论是标准输出还是错误输出，都将以邮件形式发给用户。文件里的每一个请求必须包含以spaces和tabs分割的六个域。前五个字段可以取整数值，指定何时开始工作，第六个域是字符串，称为命令字段，其中包括了crontab调度执行的命令。   
第一道第五个字段的整数取值范围及意义是：   
0～59 表示分   
1～23 表示小时   
1～31 表示日   
1～12 表示月份   
0～6 表示星期（其中0表示星期日）   
/usr/lib/cron/cron.allow表示谁能使用crontab命令。如果它是一个空文件表明没有一个用户能安排作业。如果这个文件不存在，而有另外一个文件/usr/lib/cron/cron.deny,则只有不包括在这个文件中的用户才可以使用crontab命令。如果它是一个空文件表明任何用户都可安排作业。两个文件同时存在时cron.allow优先，如果都不存在，只有超级用户可以安排作业。