Linux date 命令的格式技巧

发表 admin at 2024年8月26日

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该date命令很简单。但是，它有几个有用的选项可以增强它的功能。它还能够为您提供有关过去或未来日期的实用信息。本文向您展示了一些用于操作命令date输出的格式控件。在文章的最后，我提供了一些关于如何将此命令与常见任务结合使用的实用建议。

日期的基本语法

该命令的最基本语法date是简单地输入命令，不带任何选项和格式控制。以下是该命令及其结果输出的示例：

该命令的一个修改date是-u选项。此选项将输出转换为协调世界时 (UTC)。以下是示例：

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格式控件

当您开始添加格式控件时，命令的真正自定义date才会发生。控件可以对输出字段进行排序、管理缩写、设置屏幕上或文件中的日期格式等。在文章的最后，我将展示一些如何使用的示例date，您将看到控制格式是多么有用。

基本格式控制语法

使用一个或多个格式控件来显示信息。以下是一般语法：

# date +%<format-option>

我们来看几个例子。

标注输出字段

如果希望输出带标签，可以使用以下格式：

更改字段的顺序

您可以更改字段的显示顺序。这是最有用的自定义功能之一，date因为它允许您以最有用或最熟悉的格式显示输出。以下是其中一种方法：

下面是另一个示例：

此示例反转了结果：

在字段之间使用破折号、斜线或空格

也许您需要格式化date输出以满足特定标准，例如用破折号、斜线或空格字符分隔的日期信息。以下是几个不同的例子：

Display information from outside my current locale or time zone

It's embarrassing to say, but for whatever reason, time zones completely mess with my mind. They always have and they probably always will. That's why I was excited to discover that the date command can save me from having to visualize the sun's position over a particular geographical location to figure out the appropriate time zone.

First, you must know the name of the time zone you wish to check. You can use the timedatectl list-timezones command to display this information.

Next, combine the TZ value with the date command to display the time zone's time and date information. To show the time on the east coast of the US, run this command:

TZ and date display the time in the specified time zone, while the current date output represents the configured time zone.

Run the following command to display the time in Tokyo:

Output of the TZ='Pacific/Tokyo' date command, displaying the time in Tokyo, Japan.

Display future time/date

What if you're coordinating a meeting with someone on the east coast of the US, and you want to confirm or display a particular future time? You can use the date command to display that information.

First, you could display the date and time information for next Friday:

Display the date of the next Friday on the calendar by using the date --date="next fri" command.

Here is an example that displays the local time for 10 AM next Friday on the east coast of the US:

Output of the date --date='TZ="America/New_York" 10:00 next fri" that displays what the local time will be compared to 10:00 next Friday in New York.

Display past dates

You can also use date to display past information.

Output from the date --date="5 year ago" command showing the date and time from five years in the past.

This example shows time and date information from 15 days ago:

Output from the date --date="15 day ago" command displaying time and date information from 15 days in the past.

Practical application

It's one thing to know these tricks when using the date command, but it's another to understand how to apply them. Here are a few straightforward scenarios to get you thinking about your own tasks where date might be useful.

Redirect

You can redirect the date command into a text file. You can use any of the format controls above to customize the output. For example, what if you are conducting a very simple server documentation project? You might use the following commands:

Output from a series of system inventory commands, including date.

Set a date alias

Do you prefer the date and time to be displayed in a specific format different from the default? Set an alias for date that shows the information the way you like it. You can do this in your ~/.bashrc file.

Set an alias for the string "today" in the ~/.bashrc file to display formatted date command output.

Output of the "today" alias displaying the formatted date output.

Set the format as a variable

You can also set the date configuration as a variable on your system.

Declare the "today" variable as $(date +%d/%m/%Y) for use in a script.

Create a template file, then copy/paste the content into scripts depending on the format desired

Perhaps you create or manage various scripts, and the date output is needed in several of them. However, the date format must be different in each script. You could create a master template file that stores the required formats and then copy/paste the appropriate template into your new scripts.

Create a template that stores commonly-used date command formats to be copied into scripts, etc.

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Wrap up

Like many things in Linux, the date command is simple but also very flexible. You can control the format of the data that returned to you, ensuring you get the information you need as efficiently as possible. How have you used the date command to make your life easier?