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@ -1,5 +1,5 @@
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[#]: collector: (lujun9972)
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[#]: translator: ( )
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[#]: translator: (HankChow)
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[#]: reviewer: ( )
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[#]: publisher: ( )
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[#]: subject: (3 implications of serverless)
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@ -1,128 +0,0 @@
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Translating by Guevaraya
|
||||
|
||||
'Getting to Done' on the Linux command line
|
||||
======
|
||||
|
||||
|
||||
There is a lot of talk about getting things done at the command line. How many articles are there about using obscure flags with `ls`, nifty regular expressions with Sed and Awk, and how to parse out lots of text with Perl? That isn't what this is about.
|
||||
|
||||
This is about [Getting _to_ Done][1], making sure that the stuff we have to do actually gets tracked and done using tools that don't require a graphical desktop, a web browser, or an internet connection. To do this, we'll look at four ways of tracking your to-do list: plaintext files, Todo.txt, TaskWarrior, and Org-mode.
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|
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### Plain (and simple) text
|
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|
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|
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![plaintext][3]
|
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|
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I like to use Vim, but you can use Nano too.
|
||||
|
||||
The most straightforward way to manage your to-do list is using a plaintext file in your editor of choice. Just open an empty file and add tasks, one per line. When you are done, delete the line. Simple, effective, and it doesn't matter what you use to do it. There are a couple of drawbacks to this method, though. Once you delete a line and save the file, it is gone forever. That can be a problem if you have to report on what you have done this week or last week. And while using a simple file is flexible, it can also get cluttered really easily.
|
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|
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### Todo.txt: Plaintext leveled up
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|
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|
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![todo.txt screen][5]
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|
||||
Neat, organized, and easy to use
|
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|
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That leads us to the [Todo.txt][6] file format and application. Installation is simple—[download][7] the latest release from GitHub and run `sudo make install` from the unpacked archive.
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|
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|
||||
![Installing todo.txt][9]
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|
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It works from a Git clone as well.
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|
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Todo.txt makes it very easy to add tasks, list tasks, and mark them as done:
|
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|
||||
| `todo.sh add "Some Task"` | add "Some Task" to my todo list |
|
||||
| `todo.sh ls` | list all my tasks |
|
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| `todo.sh ls due:2018-02-15` | list all tasks due on February 15, 2018 |
|
||||
| `todo.sh do 3` | mark task number 3 as "done" |
|
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|
||||
The actual list is still in plaintext, and you can edit it with your favorite text editor as long as you follow the [correct format][10].
|
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|
||||
There is also a very robust help built into the application.
|
||||
|
||||
|
||||
![Syntax highlighting in todo.txt][12]
|
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|
||||
You can even get syntax highlighting.
|
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|
||||
There is also a large selection of add-ons, as well as specifications for writing your own. There are even browser extensions, mobile apps, and desktop apps that support the Todo.txt format.
|
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|
||||
|
||||
![GNOME extensions in todo.txt][14]
|
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|
||||
Even GNOME extensions.
|
||||
|
||||
The biggest drawback to Todo.txt is the lack of an automatic or built-in synchronization mechanism. Most (if not all) of the browser extensions and mobile apps require Dropbox to perform synchronization between the app and the copy on your desktop. If you would like something with sync built-in, we have...
|
||||
|
||||
### Taskwarrior: Now we're cooking with Python
|
||||
|
||||
[Taskwarrior][15] is a Python application with many of the same features as Todo.txt. However, it stores the data in a database and has built-in synchronization capabilities. It also keeps track of what is next, notes how old tasks are, and will warn you if you have something more important to do than what you just did.
|
||||
|
||||
[Installation][16] of Taskwarrior can be done either with your distribution's package manager, through Python's `pip` utility, or built from source. Using it is also pretty straightforward, with commands similar to Todo.txt:
|
||||
|
||||
| `task add "Some Task"` | Add "Some Task" to the list |
|
||||
| `task list` | List all tasks |
|
||||
| `task list due ``:today` | List all tasks due on today's date |
|
||||
| `task do 3` | Complete task number 3 |
|
||||
|
||||
Taskwarrior also has some pretty nice text user interfaces.
|
||||
|
||||
![Taskwarrior in Vit][18]
|
||||
|
||||
I like Vit, which was inspired by Vim.
|
||||
|
||||
Unlike Todo.txt, Taskwarrior can synchronize with a local or remote server. A very basic synchronization server called `taskd` is available if you wish to run your own, and there are several services available if you do not.
|
||||
|
||||
Taskwarrior also has a thriving and extensive ecosystem of add-ons and extensions, as well as mobile and desktop apps.
|
||||
|
||||
![Taskwarrior on GNOME][20]
|
||||
|
||||
Taskwarrior looks really nice on GNOME.
|
||||
|
||||
The only disadvantage to Taskwarrior is that, unlike the other programs listed here, you cannot directly modify the to-do list itself. You can export the task list to various formats, modify the export, and then re-import the files, but it is a lot clunkier than just opening the file directly in a text editor.
|
||||
|
||||
Which brings us to the most powerful of them all...
|
||||
|
||||
### Emacs Org-mode: Hulk smash tasks
|
||||
|
||||
![Org-mode][22]
|
||||
|
||||
Emacs has everything.
|
||||
|
||||
Emacs [Org-mode][23] is by far the most powerful, most flexible open source to-do list manager out there. It supports multiple files, uses plaintext, is almost infinitely customizable, and understands calendars, due dates, and schedules. It is also significantly more complicated to set up than the other applications listed here. But once it is set up, it does everything the other applications do and more. If you are familiar with or a fan of [Bullet Journals][24], Org-mode is possibly the closest you can get on a computer.
|
||||
|
||||
Org-mode will run anywhere Emacs runs, and there are a few mobile applications that can interact with it as well. Unfortunately, there are no desktop apps or browser extensions that support Org. Despite all that, Org-mode is still one of the best applications for tracking your to-do list, since it is so very powerful.
|
||||
|
||||
### Choose your tool
|
||||
|
||||
In the end, the goal of all these programs is to help you track what you need to do and make sure you don't forget to do something. While they all have the same basic functions, choosing which one is right for you depends on a lot of factors. Do you want synchronization built-in or not? Do you need a mobile app? Do any of the add-ons include a "must have" feature? Whatever your choice, remember that the program alone cannot make you more organized, but it can help.
|
||||
|
||||
--------------------------------------------------------------------------------
|
||||
|
||||
via: https://opensource.com/article/18/2/getting-to-done-agile-linux-command-line
|
||||
|
||||
作者：[Kevin Sonney][a]
|
||||
译者：[译者ID](https://github.com/译者ID)
|
||||
校对：[校对者ID](https://github.com/校对者ID)
|
||||
|
||||
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
|
||||
|
||||
[a]:
|
||||
[1]:https://www.scruminc.com/getting-done/
|
||||
[3]:https://opensource.com/sites/default/files/u128651/plain-text.png (plaintext)
|
||||
[5]:https://opensource.com/sites/default/files/u128651/todo-txt.png (todo.txt screen)
|
||||
[6]:http://todotxt.org/
|
||||
[7]:https://github.com/todotxt/todo.txt-cli/releases
|
||||
[9]:https://opensource.com/sites/default/files/u128651/todo-txt-install.png (Installing todo.txt)
|
||||
[10]:https://github.com/todotxt/todo.txt
|
||||
[12]:https://opensource.com/sites/default/files/u128651/todo-txt-vim.png (Syntax highlighting in todo.txt)
|
||||
[14]:https://opensource.com/sites/default/files/u128651/tod-txt-gnome.png (GNOME extensions in todo.txt)
|
||||
[15]:https://taskwarrior.org/
|
||||
[16]:https://taskwarrior.org/download/
|
||||
[18]:https://opensource.com/sites/default/files/u128651/taskwarrior-vit.png (Taskwarrior in Vit)
|
||||
[20]:https://opensource.com/sites/default/files/u128651/taskwarrior-gnome.png (Taskwarrior on GNOME)
|
||||
[22]:https://opensource.com/sites/default/files/u128651/emacs-org-mode.png (Org-mode)
|
||||
[23]:https://orgmode.org/
|
||||
[24]:http://bulletjournal.com/
|
||||
@ -1,129 +0,0 @@
|
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Translating by Jamskr
|
||||
|
||||
Coupled commands with control operators in Bash
|
||||
======
|
||||
Add logic to the command line with control operators in compound commands.
|
||||
|
||||
|
||||
|
||||
Simple compound commands—such as stringing several commands together in a sequence on the command line—are used often. Such commands are separated by semicolons, which define the end of a command. To create a simple series of shell commands on a single line, simply separate each command using a semicolon, like this:
|
||||
|
||||
```
|
||||
command1 ; command2 ; command3 ; command4 ;
|
||||
```
|
||||
|
||||
You don't need to add a final semicolon because pressing the Enter key implies the end of the final command, but it's fine to add it for consistency.
|
||||
|
||||
**& &** and **||** control operators built into Bash. These two control operators provide some flow control and enable us to alter the code-execution sequence. The semicolon and the **newline** character are also considered to be Bash control operators.
|
||||
|
||||
All the commands will run without a problem—as long as no error occurs. But what happens if an error happens? We can anticipate and allow for errors using theandcontrol operators built into Bash. These two control operators provide some flow control and enable us to alter the code-execution sequence. The semicolon and thecharacter are also considered to be Bash control operators.
|
||||
|
||||
The **& &** operator simply says "if command1 is successful, then run command2." If command1 fails for any reason, command2 won't run. That syntax looks like:
|
||||
|
||||
```
|
||||
command1 && command2
|
||||
```
|
||||
|
||||
This works because every command returns a code to the shell that indicates whether it completed successfully or failed during execution. By convention, a return code (RC) of 0 (zero) indicates success and any positive number indicates some type of failure. Some sysadmin tools just return a 1 to indicate any failure, but many use other positive numerical codes to indicate the type of failure.
|
||||
|
||||
The Bash shell's **$?** variable can be checked very easily by a script, by the next command in a list of commands, or even directly by a sysadmin. Let's look at RCs. We can run a simple command and immediately check the RC, which will always pertain to the last command that ran.
|
||||
|
||||
```
|
||||
[student@studentvm1 ~]$ ll ; echo "RC = $?"
|
||||
total 284
|
||||
-rw-rw-r-- 1 student student 130 Sep 15 16:21 ascii-program.sh
|
||||
drwxrwxr-x 2 student student 4096 Nov 10 11:09 bin
|
||||
<snip>
|
||||
drwxr-xr-x. 2 student student 4096 Aug 18 10:21 Videos
|
||||
RC = 0
|
||||
[student@studentvm1 ~]$
|
||||
```
|
||||
|
||||
This RC is 0, which means the command completed successfully. Now try the same command on a directory where we don't have permissions.
|
||||
|
||||
```
|
||||
[student@studentvm1 ~]$ ll /root ; echo "RC = $?"
|
||||
ls: cannot open directory '/root': Permission denied
|
||||
RC = 2
|
||||
[student@studentvm1 ~]$
|
||||
```
|
||||
|
||||
This RC's meaning can be found in the [**ls** command's man page][1].
|
||||
|
||||
Let's try the **& &** control operator as it might be used in a command-line program. We'll start with something simple: Create a new directory and, if that is successful, create a new file in it.
|
||||
|
||||
We need a directory where we can create other directories. First, create a temporary directory in your home directory where you can do some testing.
|
||||
|
||||
```
|
||||
[student@studentvm1 ~]$ cd ; mkdir testdir
|
||||
```
|
||||
|
||||
Create a new directory in **~/testdir** , which should be empty because you just created it, and then create a new, empty file in that new directory. The following command will do those tasks.
|
||||
|
||||
```
|
||||
[student@studentvm1 ~]$ mkdir ~/testdir/testdir2 && touch ~/testdir/testdir2/testfile1
|
||||
[student@studentvm1 ~]$ ll ~/testdir/testdir2/
|
||||
total 0
|
||||
-rw-rw-r-- 1 student student 0 Nov 12 14:13 testfile1
|
||||
[student@studentvm1 ~]$
|
||||
```
|
||||
|
||||
We know everything worked as it should because the **testdir** directory is accessible and writable. Change the permissions on **testdir** so it is no longer accessible to the user **student** as follows:
|
||||
|
||||
```
|
||||
[student@studentvm1 ~]$ chmod 076 testdir ; ll | grep testdir
|
||||
d---rwxrw-. 3 student student 4096 Nov 12 14:13 testdir
|
||||
[student@studentvm1 ~]$
|
||||
```
|
||||
|
||||
Using the **grep** command after the long list ( **ll** ) shows the listing for **testdir**. You can see that the user **student** no longer has access to the **testdir** directory. Now let's run almost the same command as before but change it to create a different directory name inside **testdir**.
|
||||
|
||||
```
|
||||
[student@studentvm1 ~]$ mkdir ~/testdir/testdir3 && touch ~/testdir/testdir3/testfile1
|
||||
mkdir: cannot create directory ‘/home/student/testdir/testdir3’: Permission denied
|
||||
[student@studentvm1 ~]$
|
||||
```
|
||||
|
||||
Although we received an error message, using the **& &** control operator prevents the **touch** command from running because there was an error in creating **testdir3**. This type of command-line logical flow control can prevent errors from compounding and making a real mess of things. But let's make it a little more complicated.
|
||||
|
||||
The **||** control operator allows us to add another command that executes when the initial program statement returns a code larger than zero.
|
||||
|
||||
```
|
||||
[student@studentvm1 ~]$ mkdir ~/testdir/testdir3 && touch ~/testdir/testdir3/testfile1 || echo "An error occurred while creating the directory."
|
||||
mkdir: cannot create directory ‘/home/student/testdir/testdir3’: Permission denied
|
||||
An error occurred while creating the directory.
|
||||
[student@studentvm1 ~]$
|
||||
```
|
||||
|
||||
Our compound command syntax using flow control takes this general form when we use the **& &** and **||** control operators:
|
||||
|
||||
```
|
||||
preceding commands ; command1 && command2 || command3 ; following commands
|
||||
```
|
||||
|
||||
The compound command using the control operators may be preceded and followed by other commands that can be related to the ones in the flow-control section but which are unaffected by the flow control. All of those commands will execute without regard to anything that takes place inside the flow-control compound command.
|
||||
|
||||
These flow-control operators can make working at the command line more efficient by handling decisions and letting us know when a problem has occurred. I use them directly on the command line as well as in scripts.
|
||||
|
||||
You can clean up as the root user to delete the directory and its contents.
|
||||
|
||||
```
|
||||
[root@studentvm1 ~]# rm -rf /home/student/testdir
|
||||
```
|
||||
|
||||
How do you use Bash control operators? Let us know in the comment section.
|
||||
|
||||
--------------------------------------------------------------------------------
|
||||
|
||||
via: https://opensource.com/article/18/11/control-operators-bash-shell
|
||||
|
||||
作者：[David Both][a]
|
||||
选题：[lujun9972][b]
|
||||
译者：[译者ID](https://github.com/译者ID)
|
||||
校对：[校对者ID](https://github.com/校对者ID)
|
||||
|
||||
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
|
||||
|
||||
[a]: https://opensource.com/users/dboth
|
||||
[b]: https://github.com/lujun9972
|
||||
[1]: http://man7.org/linux/man-pages/man1/ls.1.html
|
||||
@ -0,0 +1,128 @@
|
||||
享受Linux下命令行全操作
|
||||
======
|
||||
|
||||
|
||||
很多文章讨论关于命令行下如何做事情。有多少文章要么用晦涩的方式介绍 `ls` ，要么介绍关于 Sed 和 Awk 一些有意思的正则表达式，要么就是介绍一大堆的 perl 脚本是如何解析的？这些都不是命令行操作的重点。
|
||||
|
||||
本文章是关于[享受命令行全操作][1]，在我们不需要图形桌面，网络浏览器或网络连接情况下，用命令行操作能完成实际事务的跟踪。为了达到这一点，我们将介绍四个途径跟踪你的待办清单：纯文件文件，Todo.txt，TaskWarrior，Org-mode。
|
||||
|
||||
### 纯文本
|
||||
|
||||
![plaintext][3]
|
||||
|
||||
我喜欢用 Vim ，其实你也可以喜欢 Nano。
|
||||
|
||||
最直接管理管理你的待办清单的方式就是用纯文本文件来编辑。只需要打开一个空文件，每一行添加一个任务。当任务完成后，删除这一行，简单有效，不用再关心这一行之前干什么用的了。不过这个方法也有缺点，一点你删除一行并保存了文件，它就是永远消失了。如果你想知道本周或者上周都做了哪些事情，就成了问题。使用简单文本文件很方便却也容易导致混乱。
|
||||
|
||||
### Todo.txt: 纯文件的升级版
|
||||
|
||||
|
||||
![todo.txt screen][5]
|
||||
|
||||
整洁，有条理，易用
|
||||
|
||||
这就是我们要说的 [Todo.txt][6] 格式文件和应用程序。安装可从 GitHub [下载][7]最新的版本解压后并执行命令 `sudo make install`
|
||||
|
||||
![安装 todo.txt][9]
|
||||
|
||||
也可以从 Git 克隆一个。
|
||||
|
||||
Todo.txt 可以很容易的增加新任务，并能显示任务列表和已完成任务的标记:
|
||||
|
||||
|||
|
||||
| ------------- |:-------------|
|
||||
| `todo.sh add "某任务"` | 增加 "某任务" 到你的待办列表 |
|
||||
| `todo.sh ls` | 显示所有的任务 |
|
||||
| `todo.sh ls due:2018-02-15` | 显示2018-02-15之前的所有任务 |
|
||||
| `todo.sh do 3` | 标记任务3 为已完成任务 |
|
||||
|
||||
清单实际上仍然是纯文本，你可以用你喜欢的编辑器遵循[正确的格式][10]编辑它。
|
||||
|
||||
应用程序同时也内置了一个强大的帮助。
|
||||
|
||||
|
||||
![在 todo.txt 中语法高亮][12]
|
||||
|
||||
你可以使用语法高亮的功能
|
||||
|
||||
此外，还有许多附加组件可供选择，以及编写自己的附件组件规范。甚至有浏览器组件，移动设备应用程序和桌面应用程序支持 Todo.txt 的格式。
|
||||
|
||||
|
||||
![GNOME extensions in todo.txt][14]
|
||||
|
||||
GNOME的扩展组件
|
||||
|
||||
Todo.txt 最大的缺点是缺少自动或内置的同步机制。大多数（不是全部）的浏览器扩展程序和移动应用程序需要用 Dropbox 实现桌面系统和应用程序直接的数据同步。如果你想内置同步机制，我们也有……
|
||||
|
||||
### Taskwarrior: 现在我们用 Python 做事了
|
||||
|
||||
[Taskwarrior][15] 是一个与Todo.txt 有许多相同功能的 Python 工具。但不同的是它的数据保存在数据库里并具有内置的数据同步功能。它还可以跟踪即将要做的任务，可以提醒某个任务持续了多久，可以提醒你一些重要的事情应该马上去做。
|
||||
|
||||
[安装][16] Taskwarrior 可以通过通过发行版自带的包管理器，或通过 Python 命令 `pip`安装，或者用源码编译。用法也和 Todo.txt 的命令完全一样：
|
||||
|
||||
|||
|
||||
| ------------- |:-------------|
|
||||
| `task add "某任务"` | 增加 "某任务" 到任务清单 |
|
||||
| `task list` | 列出所有任务 |
|
||||
| `task list due ``:today` |列出截止今天的任务 |
|
||||
| `task do 3` | 标记编号是3的任务为完成状态 |
|
||||
|
||||
Taskwarrior 还有漂亮的文本用户界面。
|
||||
|
||||
![Taskwarrior in Vit][18]
|
||||
|
||||
我喜欢 Vit, 它的设计灵感来自 Vim.
|
||||
|
||||
不同于 Todo.txt，Taskwarrior 可以和本地或远程服务器同步信息。如果你希望运行自己的同步服务器可以使用名为 `taskd` 的基础服务器，如果不使用自己的服务器也有好几个可用服务器。
|
||||
|
||||
Taskwarriot 还拥有一个蓬勃发展的插件和扩展生态系统，这和移动和桌面系统的应用生态类似。
|
||||
|
||||
![GNOME in Taskwarrior ][20]
|
||||
|
||||
在 GNOME 下的 Taskwarrior 看起来还是很漂亮的。
|
||||
|
||||
Taskwarrior 有一个唯一的缺点，你是不能直接修改待办任务的，这和其他的工具不一样。你只能把任务清单按照格式导出，然后修改导出文件后，重新再导入，这样相对于编辑器直接编辑任务还是挺麻烦的。
|
||||
|
||||
谁能给我们带来最大的希望呢......
|
||||
|
||||
### Emacs Org-mode: 牛逼的任务收割机
|
||||
|
||||
![Org-mode][22]
|
||||
|
||||
Emacs 具有所有优点。
|
||||
|
||||
Emacs [Org-mode][23] 是目前为止最强大，最灵活的开源待办任务管理器。它支持多文件，使用纯文本，高度定制和自动识别日期，截止日期和任务计划。相对于我们这里介绍的其他工具，它的配置也更复杂一些。但是一旦配置好，她可以比其他工具完成更多功能。如果你是熟悉或者是 [Bullet Journals][24] 的粉丝，Org-mode 可能是在桌面程序里最像[Bullet Journals][24]的了。
|
||||
|
||||
Org-mode 可以运行在任何 Emacs 运行的地方，一些移动应用程序可以和它很好交互。但是不幸的是，目前没有桌面程序或浏览器插件支持Org-mode。尽管如此，Org-mode仍然是跟踪待办事项最好的应用程序之一，因为他确实很强大。
|
||||
|
||||
### 选择适合自己的工具
|
||||
|
||||
最后，这些程序目的是帮助你跟踪待办事务并确保不会忘记做某个事情。这些程序的基础功能都大同小异，那一款适合你取决于多种因素。有的人需要自带同步功能，有的人需要一个移动客户端，有的人要必须支持插件。不管你选择什么，请记住程序本身不会让你更有调理，但是可以帮助你。
|
||||
|
||||
--------------------------------------------------------------------------------
|
||||
|
||||
via: https://opensource.com/article/18/2/getting-to-done-agile-linux-command-line
|
||||
|
||||
作者：[Kevin Sonney][a]
|
||||
译者：[guevaraya](https://github.com/guevaraya)
|
||||
校对：[校对者ID](https://github.com/校对者ID)
|
||||
|
||||
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
|
||||
|
||||
[a]:https://opensource.com/users/ksonney (Kevin Sonney)
|
||||
[1]:https://www.scruminc.com/getting-done/
|
||||
[3]:https://opensource.com/sites/default/files/u128651/plain-text.png (plaintext)
|
||||
[5]:https://opensource.com/sites/default/files/u128651/todo-txt.png (todo.txt screen)
|
||||
[6]:http://todotxt.org/
|
||||
[7]:https://github.com/todotxt/todo.txt-cli/releases
|
||||
[9]:https://opensource.com/sites/default/files/u128651/todo-txt-install.png (Installing todo.txt)
|
||||
[10]:https://github.com/todotxt/todo.txt
|
||||
[12]:https://opensource.com/sites/default/files/u128651/todo-txt-vim.png (Syntax highlighting in todo.txt)
|
||||
[14]:https://opensource.com/sites/default/files/u128651/tod-txt-gnome.png (GNOME extensions in todo.txt)
|
||||
[15]:https://taskwarrior.org/
|
||||
[16]:https://taskwarrior.org/download/
|
||||
[18]:https://opensource.com/sites/default/files/u128651/taskwarrior-vit.png (Taskwarrior in Vit)
|
||||
[20]:https://opensource.com/sites/default/files/u128651/taskwarrior-gnome.png (Taskwarrior on GNOME)
|
||||
[22]:https://opensource.com/sites/default/files/u128651/emacs-org-mode.png (Org-mode)
|
||||
[23]:https://orgmode.org/
|
||||
[24]:http://bulletjournal.com/
|
||||
@ -0,0 +1,125 @@
|
||||
Bash 中使用控制运算符连接命令
|
||||
======
|
||||
在命令行中，使用控制运算符为复合命令添加逻辑。
|
||||
|
||||
|
||||
|
||||
一些简单的复合指令——比如说在一个命令行中连接几个命令——是经常使用的。这些命令使用分号分隔，表示一个命令结束。为了在一个命令行中创建一系列简单的 shell 命令，只需要使用分号把每一条命令分隔开，就像下面这样：
|
||||
|
||||
```
|
||||
command1 ; command2 ; command3 ; command4 ;
|
||||
```
|
||||
|
||||
最后一个分号你可以不用添加，因为当你按下回车键时就表示一个命令的结束，但是为了和其它的保持一致，还是建议加上比较好。
|
||||
|
||||
所有的命令执行都没有什么问题——只要没有什么意外发生。但是当出问题时到底发生了什么呢？我们可以预测，并且通过 Bash 中内置的 `&&` 和 `||` 运算符跟踪这些错误。这两个控制运算符提供了一些流控制，可以让我们改变代码执行队列的顺序。分号和 **换行符** 也被认为是 Bash 的控制运算符。
|
||||
|
||||
`&&` 运算符意义简单来说就是“如果 `command1` 执行成功，就接着执行 `command2`。”如果 `command1` 因为任何原因执行失败，那么 `command2` 将不执行。这个语法看下来像这样：
|
||||
|
||||
```
|
||||
command1 && command2
|
||||
```
|
||||
|
||||
这样写是允许的，因为每一个命令都会返回一个值给 shell 来表示这个命令在执行的过程中是否执行成功或者失败。通常，返回值是 0 表示成功，而一个正数值表示不同种类的错误。有一些系统管理工具仅仅返回一个 1 来表示所有的错误，但是也有很多工具使用其它的正数的返回值来表示各种类型错误。
|
||||
|
||||
我们可以很容易的使用脚本， 命令列表中的下一个命令，或者可以直接使用系统管理工具来检查 shell 变量 `$?` 。我们一起来看这些返回值。运行一个简单的命令然后立即检查它的返回值，这个返回值始终是属于最后一个运行的命令。
|
||||
|
||||
```
|
||||
[student@studentvm1 ~]$ ll ; echo "RC = $?"
|
||||
total 284
|
||||
-rw-rw-r-- 1 student student 130 Sep 15 16:21 ascii-program.sh
|
||||
drwxrwxr-x 2 student student 4096 Nov 10 11:09 bin
|
||||
<snip>
|
||||
drwxr-xr-x. 2 student student 4096 Aug 18 10:21 Videos
|
||||
RC = 0
|
||||
[student@studentvm1 ~]$
|
||||
```
|
||||
|
||||
这个返回值是 0，表示这个命令执行成功了。现在尝试使用同样的命令在一些我们没有权限的目录上。
|
||||
|
||||
```
|
||||
[student@studentvm1 ~]$ ll /root ; echo "RC = $?"
|
||||
ls: cannot open directory '/root': Permission denied
|
||||
RC = 2
|
||||
[student@studentvm1 ~]$
|
||||
```
|
||||
|
||||
这个返回值的含义可以在 [`ls` 命令的 man 页面][1] 中找到。
|
||||
|
||||
现在我们来试试 `&&` 这个控制运算符，因为它也可能会被用在一个命令行程序中。我们将从一个简单的示例开始：创建一个新目录，如果创建成功就在这个目录中创建一个文件。
|
||||
|
||||
我们需要一个目录可以创建其它的目录。首先，在你的家目录中创建一个临时的目录用来做测试。
|
||||
|
||||
```
|
||||
[student@studentvm1 ~]$ cd ; mkdir testdir
|
||||
```
|
||||
|
||||
在 `~/testdir` 中新建一个目录，这也应该是一个空目录，因为是你刚刚创建的，然后创建一个新的，空文件在这个新目录中。下面的命令可以做这些事情。
|
||||
|
||||
```
|
||||
[student@studentvm1 ~]$ mkdir ~/testdir/testdir2 && touch ~/testdir/testdir2/testfile1
|
||||
[student@studentvm1 ~]$ ll ~/testdir/testdir2/
|
||||
total 0
|
||||
-rw-rw-r-- 1 student student 0 Nov 12 14:13 testfile1
|
||||
[student@studentvm1 ~]$
|
||||
```
|
||||
|
||||
我们看到一切都运行得很好，因为 `testdir` 目录是访问且可写的。然后我们改变 `testdir` 目录的权限，让用户 **student** 不再具有访问的权限。操作如下：
|
||||
|
||||
```
|
||||
[student@studentvm1 ~]$ chmod 076 testdir ; ll | grep testdir
|
||||
d---rwxrw-. 3 student student 4096 Nov 12 14:13 testdir
|
||||
[student@studentvm1 ~]$
|
||||
```
|
||||
|
||||
在长列表（`ll`）命令后面使用 `grep` 命令来列出 `testdir` 目录。你可以看到用户 `student` 不再有 `testdir` 目录的访问权限。现在我们像之前一样运行同样的命令，但是在 `testdir` 目录中创建的是一个不同的目录。
|
||||
|
||||
```
|
||||
[student@studentvm1 ~]$ mkdir ~/testdir/testdir3 && touch ~/testdir/testdir3/testfile1
|
||||
mkdir: cannot create directory ‘/home/student/testdir/testdir3’: Permission denied
|
||||
[student@studentvm1 ~]$
|
||||
```
|
||||
|
||||
尽管我们也同样得到了一个错误的消息，但 `&&` 控制运算符阻止了 `touch` 命令的运行，因为在创建 `testdir3` 目录的时候发生了错误。通过这种复合的流控制可以阻止一些错误的发生使事情变乱。但是这样看起来变得稍微复杂了一些。
|
||||
|
||||
`||` 控制运算符允许添加另一个命令，这个命令在初始程序语句返回值大于 0 时执行。
|
||||
|
||||
```
|
||||
[student@studentvm1 ~]$ mkdir ~/testdir/testdir3 && touch ~/testdir/testdir3/testfile1 || echo "An error occurred while creating the directory."
|
||||
mkdir: cannot create directory ‘/home/student/testdir/testdir3’: Permission denied
|
||||
An error occurred while creating the directory.
|
||||
[student@studentvm1 ~]$
|
||||
```
|
||||
|
||||
当我们使用 `&&` 和 `||` 控制运算符时，使用流控制的复合命令的语法格式通常是下面这样的形式。
|
||||
|
||||
```
|
||||
preceding commands ; command1 && command2 || command3 ; following commands
|
||||
```
|
||||
|
||||
使用控制运算符的复合命令可以在其它命令之前或者之后，这些和控制运算符流控制有关系，但是不受控制运算符流控制的影响。如果不考虑复合命令的流控制中发生的任何事情那么所有的命令都将执行。
|
||||
|
||||
当程序出问题时，这些流控制运算符使得在命令中处理出错和通知我们变得更有效率。我直接在命令行中使用它们，也在脚本中使用。
|
||||
|
||||
你可以以 root 用户的身份来删除这个目录和它里面的内容。
|
||||
|
||||
```
|
||||
[root@studentvm1 ~]# rm -rf /home/student/testdir
|
||||
```
|
||||
|
||||
你是怎样使用 Bash 控制运算符的呢？在评论区中告诉我们。
|
||||
|
||||
--------------------------------------------------------------------------------
|
||||
|
||||
via: https://opensource.com/article/18/11/control-operators-bash-shell
|
||||
|
||||
作者：[David Both][a]
|
||||
选题：[lujun9972][b]
|
||||
译者：[Jamskr](https://github.com/Jamskr)
|
||||
校对：[校对者ID](https://github.com/校对者ID)
|
||||
|
||||
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
|
||||
|
||||
[a]: https://opensource.com/users/dboth
|
||||
[b]: https://github.com/lujun9972
|
||||
[1]: http://man7.org/linux/man-pages/man1/ls.1.html
|
||||
Loading…
Reference in New Issue
Block a user