July 2017
Intermediate to advanced
398 pages
11h 54m
Chinese
Content preview from Python数据处理
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314
｜
第
14
章
14.6.1
CronJobs
Cron
（
http://en.wikipedia.org/wiki/Cron
）是一个基于
Unix
系统的任务调度工具，用来使用
服务器日志和管理工具运行脚本。
Cron
需要你确定任务执行的频率和时间。
如果你不能轻松地为脚本确定一个时间线，
cron
可能不是一个好的选择。另
外，你可以运行一个规律的
cron
任务来测试是否存在运行任务所必需的条
件，然后使用一个数据库或本地文件通知运行的时间。在多个定时任务的帮
助下，你可以检查文件或数据库，并且执行任务。
如果你之前从来没有使用过
cron
文件，它们非常直观。大多数的任务可以通过输入下面的
指令来编辑：
crontab -e
取决于操作系统，如果之前从来没有编写过
cron
文件，你可能会收到提示，
让你选择一个编辑器。你可以使用默认的配置，或者根据其他的偏好改变
它。
你会在文件中看到一些文档和注释，解释
cron
文件是如何工作的。
cron
文件中每一个不以
#
符号开头的行，都定义了一个
cron
任务。每一个
cron
任务都需要下面这个参数列表：
minute hour day_of_month month day_of_week usercommand
如果脚本需要在一天中的每个小时都执行，但是只在工作日执行，你需要写类似于下面的
代码：
0 * * * 1-5 python run_this.py
这告诉
cron
在周一到周五的每个整点开始执行脚本。有很多好的入门教程（
https://help.
ubuntu.com/community/CronHowto ...
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