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[Translated] Linux date command - Display and Set System Date and Time
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Translating-----------geekpi
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Linux date command – Display and Set System Date and Time
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================================================================================
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Date on the operating system may only be considered as a timepiece. Especially on console mode, we do generally not see date as an important think. But for Administrator, this assumption is false. Do you know that a wrong date and time can make you can’t compile an application?
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Because date and time is important, this is may be the reason why Network Time Protocol is developed. Let’s start to see what date command do for you.
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### Display system date ###
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To display your system date, just type
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$ date
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Thu Dec 5 22:55:41 WIB 2013
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### Formatting Date ###
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Date come with many formats. If you are unhappy with default format you can change it. You may think “Why I need to change the format? A default output is enough for me”.
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Yes. It is true. But when you do programming, default output may not meet the user need. So here’s some custom outputs.
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### Output date and time in RFC 2822 format ###
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$ date -R
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Thu, 05 Dec 2013 23:40:53 +0700
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**RFC 2822** has a format like this : **day, date-month-year, hours:minutes:second timezone**
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Timezone +0700 is same with GMT +7
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By default **date** is using the timezone which defined in **/etc/localtime**. Valid timezones data are defined in **/usr/share/timezones**
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### Print or set Coordinated Universal Time ###
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From [Wikipedia][1], UTC means
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> The primary standard which the world regulates clocks and time. It is one several closely related successors to Greenwich Mean Time.
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To display your date and time with UTC format, use -u parameter
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$ date -u
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Thu Dec 5 16:45:58:UTC 2013
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### Using formatting options ###
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To custom your date format, **use a plus sign (+)**
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$ date +”Day : %d Month : %m Year : %Y”
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Day: 05 Month: 12 Year: 2013
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$ date +%D
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12/05/13
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**%D** format follows **Year/Month/Day format**.
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You can also put the day name if you want. Here’s some examples :
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$ date +”%a %b %d %y”
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Fri 06 Dec 2013
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$ date +”%A %B %d %Y”
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Friday December 06 2013
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$ date +”%A %B %d %Y %T”
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Friday December 06 2013 00:30:37
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$ date +”%A %B-%d-%Y %c”
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Friday December-06-2013 12:30:37 AM WIB
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There are still a lot of format options available. Just type
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$ date –help
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Or
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$ man date
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To show date command syntax and parameters.
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So basically, date command will interpret all percent sign (%) and print anything inside a quotes sign (“ “)
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### Set system date and time ###
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Generally, you want your system date and time is set automatically. If for some reason you have to change it manually, we can use this command :
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# date –set=”20140125 09:17:00”
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It will **set** your current date and time of your system into **January 25, 2014 and 09:17:00 AM. Please note**, that you **must** have root privilege to do this. Otherwise you will have an error message like this :
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date: cannot set date: Operation not permitted
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Sat Jan 25 09:17:00 WIB 2014
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### Reset your time back ###
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If you need to reset your system date and time back to the original, you can do this trick.
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# hwclock
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Fri 06 Dec 2013 03:44:10 AM WIB -0.314082 seconds
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And set your system date and time to the output of hwclock command.
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### Using date command on a script ###
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Remember when I said before about why you may need to change the date output? One of the answer may be because you do programming. Let’s see an example on bash script.
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$ vi display.date
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#! /bin/bash
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DATETIME=$(date +”DATE: %a %b-%d-%Y TIME: %T WEEK NUMBER: %W”)
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echo $DATETIME
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Save it and run it using :
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$ ./display.date
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DATE : Fri Dec-06-2013 TIME: 03:08:19 WEEK Number :40
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If you find error permission denied error message, type :
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$ chmod 755 display.date
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### Using date on a backup procedure ###
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Another example is when you are using date on a backup procedure.
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$ date +%F
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2013-12-06
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$ tar zcfv /daily_backup/backup-`date +%F`.tar.gz /home/pungki/Documents
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It will compress folder **/home/pungki/Documents** into a a file with name **backup-2013-12-06.tar.gz** which located in **/daily_backup folder**.
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### Conclusion ###
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Date may be seen as something that is not important. But dates play an important role. As usual, to have more detail in using date command, please visit date manual page by typing man date in your console.
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--------------------------------------------------------------------------------
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via: http://linoxide.com/linux-command/date-command-linux/
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译者：[译者ID](https://github.com/译者ID) 校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创翻译，[Linux中国](http://linux.cn/) 荣誉推出
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[1]:http://en.wikipedia.org/wiki/Coordinated_Universal_Time
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@ -0,0 +1,142 @@
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Linux date命令 - 显示和设置系统日期与时间
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================================================================================
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操作系统上的时间或许只被认为是时钟。特别在控制台下, 我们通常不认为date重要。但是对于管理员,这个假设是错误的。你知道错误的日期和时间会使你不能编译程序么?
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因为日期和时间的重要,这或许就是开发网络时间协议(Network Time Protocol)的原因。让我们开始了解date命令是如何工作的。
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### 显示系统日期 ###
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要显示系统日期,只要输入:
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$ date
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Thu Dec 5 22:55:41 WIB 2013
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### 格式化日期 ###
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日期有很多格式。如果你不喜欢默认的格式,你可以转换它。你可能会想"为什么我需要改变格式? 默认的输出对我足够了。" 是这样的。但是当你在编程时,默认输出或许无法满足用户的需求。因此这里有一些自定义输出。
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### RFC 2822 的日期与时间输出格式 ###
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$ date -R
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Thu, 05 Dec 2013 23:40:53 +0700
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**RFC 2822** 的格式像这样 : **星期, 日-月-年, 小时:分钟:秒 时区**
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时区 +0700 等同于 GMT +7。
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默认上**date**使用的是定义在**/etc/localtime**的时区。有效时区数据定义在**/usr/share/timezones**。
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### 打印或者设置协调世界时 ###
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在 [Wikipedia][1]上, UTC 意思是
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> 主要的调节世界时钟和时间的标准。这是格林位置标准时间几个非常相近的继任者之一。
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以UTC形式显示日期和时间, 使用 -u 参数
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$ date -u
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Thu Dec 5 16:45:58:UTC 2013
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### 使用格式化选项 ###
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要自定义你的日期格式, **使用加号 (+)**
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$ date +”Day : %d Month : %m Year : %Y”
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Day: 05 Month: 12 Year: 2013
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$ date +%D
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12/05/13
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**%D** 格式遵循 **年/月/日 的格式**.
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如果你想的话,你可以输出日期的名字。下面是一些例子:
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$ date +”%a %b %d %y”
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Fri 06 Dec 2013
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$ date +”%A %B %d %Y”
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Friday December 06 2013
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$ date +”%A %B %d %Y %T”
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Friday December 06 2013 00:30:37
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$ date +”%A %B-%d-%Y %c”
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Friday December-06-2013 12:30:37 AM WIB
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还有很多的日期格式。只要输入:
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$ date –help
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或者
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$ man date
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来显示date命令的语法和参数。
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基本上,date命令会翻译所有所有的百分号(%)和打印打印在引号("")内所有的内容。
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### 设置系统日期和时间 ###
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通常地,你希望你的系统日期和时间是自动设置的。如果由于一些原因,你想要手动修改它,我们可以使用这个命令。
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# date –set=”20140125 09:17:00”
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这会**设置**你当前的系统日期和时间到**一月 25, 2014 and 09:17:00 AM。请注意**,你**必须**拥有特权来这么做。不然你会得到这样一个错误。
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date: cannot set date: Operation not permitted
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Sat Jan 25 09:17:00 WIB 2014
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### 重置你的时间 ###
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如果你希望重置你的系统日期和时间到原始值,你可以用这个技巧。
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# hwclock
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Fri 06 Dec 2013 03:44:10 AM WIB -0.314082 seconds
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这回设置你的系统日期和时间到hwclock命令的输出的样子
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### 在脚本中使用date命令 ###
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还记得我之前说为什么你需要改变date的输出么?一个答案是你或许需要编程。让我们看下bash脚本下的一个例子。
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$ vi display.date
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#! /bin/bash
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DATETIME=$(date +”DATE: %a %b-%d-%Y TIME: %T WEEK NUMBER: %W”)
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echo $DATETIME
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保存并运行它:
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$ ./display.date
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DATE : Fri Dec-06-2013 TIME: 03:08:19 WEEK Number :40
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如果你发现权限拒绝错误信息,输入:
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$ chmod 755 display.date
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### 在备份流程中使用date ###
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另外一个例子是子你备份流程中使用date。
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$ date +%F
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2013-12-06
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$ tar zcfv /daily_backup/backup-`date +%F`.tar.gz /home/pungki/Documents
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它会压缩文件夹**/home/pungki/Documents**到一个位于**/daily_backup folder**的文件**backup-2013-12-06.tar.gz**中。
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### 总结 ###
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date可能被认为在某些方面不重要。但是date扮演了一个重要的角色。通常上,要想知道关于date命令更多的细节,在你的控制台下输入man date访问man页面。
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--------------------------------------------------------------------------------
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via: http://linoxide.com/linux-command/date-command-linux/
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译者：[geekpi](https://github.com/geekpi) 校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创翻译，[Linux中国](http://linux.cn/) 荣誉推出
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[1]:http://en.wikipedia.org/wiki/Coordinated_Universal_Time
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