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4 terminal applications with great command-line UIs
============================================================
### We look at a few well-designed CLI programs and how they overcome some discoverability problems.
![4 awesome command-line tools](https://opensource.com/sites/default/files/styles/image-full-size/public/images/life/code_computer_development_programming.png?itok=wMspQJcO "4 awesome command-line tools")
>Image by : opensource.com
In this article, I'll look at a shortcoming of command-line interfaces—discoverability—and a few ways to overcome this problem.
I love command lines. My first command line was DOS 6.2, back in 1997\. I learned the syntax for various commands and showed off how to list hidden files in a directory (**attrib**). I would carefully craft my commands one character at a time. When I made a mistake, I would proceed to retype the command from the beginning. One fine day someone showed me how to traverse the history using the up and down arrow keys and I was blown away.
Programming and development
* [New Python content][1]
* [Our latest JavaScript articles][2]
* [Recent Perl posts][3]
* [Red Hat Developers Blog][4]
Later when I was introduced to Linux, I was pleasantly surprised that up and down arrows retained their ability to traverse the history. I was still typing each character meticulously, but by now I knew how to touch type and I was doing exceedingly well with my 55 words per minute. Then someone showed me tab-completion and changed my life once again.
In GUI applications menus, tool tips and icons are used to advertise a feature for the user. Command lines lack that ability, but there are ways to overcome this problem. Before diving into solutions, I'll look at a couple of problematic CLI apps:
### 1\. MySQL
First we have our beloved MySQL REPL. I often find myself typing **SELECT * FROM** and then press **Tab** out of habit. MySQL asks whether I'd like to see all 871 possibilities. I most definitely don't have 871 tables in my database. If I said **yes**, it shows a bunch of SQL keywords, tables, functions, and so on.
![MySQL gif](https://opensource.com/sites/default/files/mysql.gif)
### 2\. Python
Let's look at another example, the standard Python REPL. I start typing a command and press the **Tab** key out of habit. Lo and behold a **Tab** character is inserted, which is a problem considering that a **Tab** character has no business in a Python source code.
![Python gif](https://opensource.com/sites/default/files/python.gif "Python gif")
### Good UX
Now let's look at well-designed CLI programs and how they overcome some discoverability problems.
### Auto-completion: bpython
[Bpython][15] is a fancy replacement for the Python REPL. When I launch bpython and start typing, suggestions appear right away. I haven't triggered them via a special key combo, not even the famed **Tab** key.
![bpython gif](https://opensource.com/sites/default/files/bpython.gif "bpython gif")
When I press the **Tab** key out of habit, it completes the first suggestion from the list. This is a great example of bringing discoverability to CLI design.
The next aspect of bpython is the way it surfaces documentation for modules and functions. When I type in the name of a function, it presents the function signature and the doc string attached with the function. What an incredibly thoughtful design.
### Context-aware completion: mycli
[Mycli][16] is a modern alternative to the default MySQL client. This tool does to MySQL what bpython does to the standard Python REPL. Mycli will auto-complete keywords, table names, columns, and functions as you type them.
The completion suggestions are context-sensitive. For example, after the **SELECT * FROM**, only tables from the current database are listed in the completion, rather than every possible keyword under the sun.
![mycli gif](https://opensource.com/sites/default/files/mycli.gif "mycli gif")
### Fuzzy search and online Help: pgcli
If you're looking for a PostgreSQL version of mycli, check out [pgcli][17]. As with mycli, context-aware auto-completion is presented. The items in the menu are narrowed down using fuzzy search. Fuzzy search allows users to type sub-strings from different parts of the whole string to try and find the right match.
![pgcli gif](https://opensource.com/sites/default/files/pgcli.gif "pgcli gif")
Both pgcli and mycli implement this feature in their CLI. Documentation for slash commands are presented as part of the completion menu.
### Discoverability: fish
In traditional Unix shells (Bash, zsh, etc.), there is a way to search your history. This search mode is triggered by **Ctrl-R**. This is an incredibly useful tool for recalling a command you ran last week that starts with, for example, **ssh** or **docker**. Once you know this feature, you'll find yourself using it often.
If this feature is so useful, why not do this search all the time? That's exactly what the [**fish** shell][18] does. As soon as you start typing a command, **fish** will start suggesting commands from history that are similar to the one you're typing. You can then press the right arrow key to accept that suggestion.
### Command-line etiquette
I've reviewed innovative ways to solve the discoverability problems, but there are command-line basics everyone should implement as part of the basic REPL functionality:
* Make sure the REPL has a history that can be recalled via the arrow keys. Make sure the history persists between sessions.
* Provide a way to edit the command in an editor. No matter how awesome your completions are, sometimes users just need an editor to craft that perfect command to drop all the tables in production.
* Use a pager to pipe the output. Don't make the user scroll through their terminal. Oh, and use sane defaults for your pager. (Add the option to handle color codes.)
* Provide a way to search the history either via the **Ctrl-R** interface or the **fish**-style auto-search.
### Conclusion
In part 2, I'll look at specific libraries in Python that allow you to implement these techniques. In the meantime, check out some of these well-designed command-line applications:
* [bpython][5] or [ptpython][6]: Fancy REPL for Python with auto-completion support.
* [http-prompt][7]: An interactive HTTP client.
* [mycli][8]: A command-line interface for MySQL, MariaDB, and Percona with auto-completion and syntax highlighting.
* [pgcli][9]: An alternative to [psql][10] with auto-completion and syntax-highlighting.
* [wharfee][11]: A shell for managing Docker containers.
_Learn more in Amjith Ramanujam's  [PyCon US 2017][12] talk, [Awesome Commandline Tools][13], May 20th in Portland, Oregon._
--------------------------------------------------------------------------------
作者简介：
Amjith Ramanujam - Amjith Ramanujam is the creator of pgcli and mycli. People think they're pretty cool and he doesn't disagree. He likes programming in Python, Javascript and C. He likes to write simple, understandable code, sometimes he even succeeds.
-----------------------
via: https://opensource.com/article/17/5/4-terminal-apps
作者：[Amjith Ramanujam ][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]:https://opensource.com/users/amjith
[1]:https://opensource.com/tags/python?src=programming_resource_menu
[2]:https://opensource.com/tags/javascript?src=programming_resource_menu
[3]:https://opensource.com/tags/perl?src=programming_resource_menu
[4]:https://developers.redhat.com/?intcmp=7016000000127cYAAQ&src=programming_resource_menu
[5]:http://bpython-interpreter.org/
[6]:http://github.com/jonathanslenders/ptpython/
[7]:https://github.com/eliangcs/http-prompt
[8]:http://mycli.net/
[9]:http://pgcli.com/
[10]:https://www.postgresql.org/docs/9.2/static/app-psql.html
[11]:http://wharfee.com/
[12]:https://us.pycon.org/2017/
[13]:https://us.pycon.org/2017/schedule/presentation/518/
[14]:https://opensource.com/article/17/5/4-terminal-apps?rate=3HL0zUQ8_dkTrinonNF-V41gZvjlRP40R0RlxTJQ3G4
[15]:https://bpython-interpreter.org/
[16]:http://mycli.net/
[17]:http://pgcli.com/
[18]:https://fishshell.com/
[19]:https://opensource.com/user/125521/feed
[20]:https://opensource.com/article/17/5/4-terminal-apps#comments
[21]:https://opensource.com/users/amjith

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4 个拥有漂亮命令行 UI 的终端程序
============================================================
### 我们来看几个精心设计的 CLI 程序，以及如何克服一些可发现的问题。
![4 awesome command-line tools](https://opensource.com/sites/default/files/styles/image-full-size/public/images/life/code_computer_development_programming.png?itok=wMspQJcO "4 awesome command-line tools")
>图片提供： opensource.com
在本文中，我会指出命令行界面的可见缺点以及克服这些问题的几种方法。
我喜欢命令行。我第一次接触命令行是在 1997 的 DOS 6.2 上。我学习了各种命令的语法，并展示了如何在目录中列出隐藏的文件（**attrib**）。我会每次仔细检查命令中的每个字符。 当我犯了一个错误，我会从头开始重新输入命令。有一天，有人向我展示了如何使用向上和向下箭头按键遍历历史，我被震惊了。
编程和开发
* [新的 Python 内容][1]
* [我们最新的 JavaScript 文章][2]
* [最近的 Perl 帖子][3]
* [红帽开发者博客][4]
后来当我被介绍 Linux 时，让我感到惊喜的是，上下箭头保留了它们遍历历史记录的能力。我仍然仔细地打字，但到现在为止，我了解如何输入，并且我能以每分钟 55 个单词的速度做的很好。接着有人向我展示了 tab 键，并再次改变了我的生活。
在 GUI 应用程序菜单中，工具提示和图标向用户展示功能。命令行缺乏这种能力，但有办法克服这个问题。在深入解决方案之前，我会来看看几个有问题的 CLI 程序：
### 1\. MySQL
首先我们有我们所钟爱的 MySQL REPL。我经常发现自己在输入 **SELECT * FROM** 然后按 **Tab** 的习惯。MySQL 会询问我是否想看到所有的 871 中可能性。我的数据库中绝对没有 871 张表。如果我选择 **yes**，它会显示一堆 SQL 关键字、表、函数等。
![MySQL gif](https://opensource.com/sites/default/files/mysql.gif)
### 2\. Python
我们来看另一个例子，标准的 Python REPL。我开始输入命令，然后习惯按 **Tab** 键。瞧，插入了一个 **Tab** 字符，考虑到 **Tab** 在 Python 中没有作用，这是一个问题。
![Python gif](https://opensource.com/sites/default/files/python.gif "Python gif")
### 好的 UX
让我看下设计良好的 CLI 程序以及它们是如何克服这些可见问题的。
### 自动补全： bpython
[Bpython][15] 是对 Python REPL 的一个很好的替代。当我运行 bpython 并开始输入时，建议会立即出现。我没用通过特殊的键盘绑定触发它，甚至没有按下 **Tab** 键。
![bpython gif](https://opensource.com/sites/default/files/bpython.gif "bpython gif")
当我出于习惯按下 **Tab** 键时，它会用列表中的第一个建议补全。这是给 CLI 设计带来可见性的一个很好的例子。
bpython 另一方面可以展示模块和函数的文档。当我输入一个函数的名字时，它会显示函数签名以及这个函数附带的文档字符串。这是一个多么令人难以置信的周到设计啊。
### 上下文感知补全：mycli
[Mycli][16]是默认的 MySQL 客户端的现代替代品。这个工具对 MySQL 来说就像 bpython 对标准 Python REPL 做的那样。Mycli 将在你输入时自动补全关键字、表名、列和函数。
补全建议是上下文相关的。例如，在 **SELECT * FROM** 之后，只有来自当前数据库的表才会列出，而不是所有可能的关键字。
![mycli gif](https://opensource.com/sites/default/files/mycli.gif "mycli gif")
### 模糊搜索和在线帮助： pgcli
如果您正在寻找 PostgreSQL 版本的 mycli，请查看 [pgcli][17]。 与 mycli 一样，它提供了上下文感知的自动补全。菜单中的项使用模糊搜索缩小。模糊搜索允许用户输入整体字符串中的任意子字符串来尝试找到正确的匹配项。
![pgcli gif](https://opensource.com/sites/default/files/pgcli.gif "pgcli gif")
pgcli 和 mycli 同时在 CLI 中实现了这个功能。斜杠命令的文档也作为补全菜单的一部分展示。
### 可发现性: fish
在传统的 Unix shell（Bash、zsh 等）中，有一种搜索历史记录的方法。此搜索模式由 **Ctrl-R** 触发。当在再次调用你上周运行的命令时，这是一个令人难以置信的有用的工具，例如 **ssh**或 **docker**。 一旦你知道这个功能，你会发现自己经常使用它。
如果这个功能是如此有用，那为什么不每次都搜索呢？这正是 [**fish** shell][18] 所做的。一旦你开始输入命令，**fish** 将开始建议与历史记录类似的命令。然后，你可以按右箭头键接受该建议。
### 命令行规矩
我已经回顾了一些创新的方法来解决可见的问题，但也有一些命令行的基础知识, 每个人都应该作为基本的 repl 功能的一部分来执行：
* 确保 REPL 有可通过箭头键调用的历史记录。确保会话之间的历史持续存在。
* 提供在编辑器中编辑命令的方法。不管你的补全是多么棒，有时用户只需要一个编辑器来制作完美的命令来删除生产环境中所有的表。
* 使用 pager 来管道输出。不要让用户滚动他们的终端。哦，并为 pager 使用合理的默认值。（添加选项来处理颜色代码。）
* 提供一种通过 **Ctrl-R** 界面或者 **fish** 样式的自动搜索来搜索历史记录的方法。
### 总结
在第 2 部分中，我将来看看 Python 中使你能够实现这些技术的特定库。同时，请查看其中一些精心设计的命令行应用程序：
* [bpython][5]或 [ptpython][6]：具有自动补全支持的 Python REPL。
* [http-prompt][7]：交互式 HTTP 客户端。
* [mycli][8]：MySQL、MariaDB 和 Percona 的命令行界面，具有自动补全和语法高亮。
* [pgcli][9]：具有自动补全和语法高亮，是对 [psql][10] 的替代工具。
* [wharfee][11]：用于管理 Docker 容器的 shell。
_在这了解 Amjith Ramanujam 更多的在 5 月 20 日在波特兰俄勒冈州举办的 [PyCon US 2017][12] 上的谈话“[令人敬畏的命令行工具][13]”。_
--------------------------------------------------------------------------------
作者简介：
Amjith Ramanujam - Amjith Ramanujam 是 pgcli 和 mycli 的创始人。人们认为它们很酷，他并不反对。他喜欢用 Python、Javascript 和 C 编程。他喜欢编写简单易懂的代码，它们有时甚至会成功。
-----------------------
via: https://opensource.com/article/17/5/4-terminal-apps
作者：[Amjith Ramanujam ][a]
译者：[geekpi](https://github.com/geekpi)
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/amjith
[1]:https://opensource.com/tags/python?src=programming_resource_menu
[2]:https://opensource.com/tags/javascript?src=programming_resource_menu
[3]:https://opensource.com/tags/perl?src=programming_resource_menu
[4]:https://developers.redhat.com/?intcmp=7016000000127cYAAQ&src=programming_resource_menu
[5]:http://bpython-interpreter.org/
[6]:http://github.com/jonathanslenders/ptpython/
[7]:https://github.com/eliangcs/http-prompt
[8]:http://mycli.net/
[9]:http://pgcli.com/
[10]:https://www.postgresql.org/docs/9.2/static/app-psql.html
[11]:http://wharfee.com/
[12]:https://us.pycon.org/2017/
[13]:https://us.pycon.org/2017/schedule/presentation/518/
[14]:https://opensource.com/article/17/5/4-terminal-apps?rate=3HL0zUQ8_dkTrinonNF-V41gZvjlRP40R0RlxTJQ3G4
[15]:https://bpython-interpreter.org/
[16]:http://mycli.net/
[17]:http://pgcli.com/
[18]:https://fishshell.com/
[19]:https://opensource.com/user/125521/feed
[20]:https://opensource.com/article/17/5/4-terminal-apps#comments
[21]:https://opensource.com/users/amjith