PHP计划任务
我们知道Linux下PHP可以很方便的实现计划任务，而Windows平台上PHP计划任务的实现比较复杂，PHP计划任务的实现在PHP WEB开发中是非常有用的，比如可以实现定时Mysql数据库备份、更新缓存、数据采集、定时生成静态页面等任务。而PHP ignore_user_abort函数可以实现当客户端中断（比如关闭游览器）后仍然继续执行任务的功能。下面来看一段通过PHP ignore_user_abort函数实现PHP计划任务的实例代码。
PHP计划任务实例代码
PHP Code 复制内容到剪贴板
PHP计划任务实例说明：在上述代码中主要功能是每隔15秒自动通过PHP文件写入操作在文件中写入一段文字，当用户关闭游览器后仍然继续执行。
第2行：首先执行php ignore_user_abort函数，告知系统忽略用户放弃行为继续执行，PHP默认情况是当远程客户端连接中断时脚本会退出。通过php ignore_user_abort 函数来控制是否忽略用户中断行为继续执行PHP代码。
知识点：ignore_user_abort(setting) setting 可选。如果设置为 true，则忽略与用户的断开，如果设置为 false，会导致脚本停止运行。如果未设置该参数，会返回当前的设置。
第3行：不限制PHP的脚本运行时间。我们知道默认PHP脚本运行都是有时间限制的，一般通过PHP.INI配置文件中的max_execution_time选项设定。通过PHP set_time_limit函数可以更改具体时间，设为0则代表不限制时间。
第4行：设定具体间隔时间，以秒为单位。
第5-21行：主要是不间断地以间隔时间为单位执行一次PHP文件写入操作。
PHP计划任务注意事项说明：在游览器中执行这段PHP代码后，除非中断WEB服务器或者关闭系统，否则后台将一直以设定的间隔时间执行这段代码。
至此，通过PHP ignore_user_abort函数实现PHP计划任务功能的实例教程就介绍完了，通过了解这个实例的实现原理，你就可以知道很多PHP博客中的定时数据库备份、定时生成静态页面等功能是如何实现的。
使用ignore_user_abort()实现php文件能够在浏览器关掉之后照样运行。
当然，要想使程序一直执行，还必须加上set_time_limit(0);
Linux 下有种更简单的方法，就是crontab命令
crontab命令的功能是在一定的时间间隔调度一些命令的执行。
crontab 使用方法： crontab [ -e | -l | -r ] 文件名 -e:编辑任务 -l:显示任务信息 -r:删除定时执行任务信息
crontab的格式：
* * * * * Command
分 时 日 月 星期 要运行的命令
crontab的例子：
*/5 * * * * lynx http://www.php100.com
每5分钟访问一次 www.php100.com
0 8 * * * lynx http://www.php100.com
每天早上8点访问 www.php100.com
0 10 6 * 1-5 lynx http://www.php100.com
每个月的6号和每个礼拜的星期一到星期五的早上10点访问 www.php100.com
0 5 7 8 * lynx http://www.php100.com
8月7日早上5点访问 www.php100.com
上面几个特殊的意思：
"*"代表所有的取值范围内的数字，"/"代表每的意思,"*/5"表示每5个单位，"-"代表从某个数字到某个数字,","分开几个离散的数字。
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