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[translated] 20171020 3 Tools to Help You Remember Linux Commands

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3 Tools to Help You Remember Linux Commands
============================================================
![apropos](https://www.linux.com/sites/lcom/files/styles/rendered_file/public/commands-main.jpg?itok=OESH_Evp "apropos")
The apropos tool, which is installed by default on nearly every Linux distribution, can help you find the command you need.[Used with permission][5]
The Linux desktop has come a very long way from its humble beginnings. Back in my early days of using Linux, knowledge of the command line was essential—even for the desktop. That’s no longer true. Many users might never touch the command line. For Linux system administrators, however, that’s not the case. In fact, for any Linux admin (be it server or desktop), the command line is a requirement. From managing networks, to security, to application and server settings—there’s nothing like the power of the good ol’ command line.
But, the thing is… there are a  _lot_ of commands to be found on a Linux system. Consider  _/usr/bin_  alone and you’ll find quite a lot of commands (you can issue  _ls /usr/bin/ | wc -l_ to find out exactly how many you have). Of course, these aren’t all user-facing executables, but it gives you a good idea of the scope of Linux commands. On my Elementary OS system, there are 2029 executables within  _/usr/bin_ . Even though I will use only a fraction of those commands, how am I supposed to remember even that amount?
Fortunately, there are various tricks and tools you can use, so that you’re not struggling on a daily basis to remember those commands. I want to offer up a few such tips that will go a long way to helping you work with the command line a bit more efficiently (and save a bit of brain power along the way).
We’ll start with a built-in tool and then illustrate two very handy applications that can be installed.
### Bash history
You may or may not know this, but Bash (the most popular Linux shell) retains a history of the commands you run. Want to see it in action? There are two ways. Open up a terminal window and tap the Up arrow key. You should see commands appear, one by one. Once you find the command you’re looking for, you can either use it as is, by hitting the Enter key, or modify it and then execute with the Enter key.
This is a great way to re-run (or modify and run) a command you’ve previously issued. I use this Linux feature regularly. It not only saves me from having to remember the minutiae of a command, it also saves me from having to type out the same command over and over.
Speaking of the Bash history, if you issue the command  _history_ , you will be presented with a listing of commands you have run in the past (Figure 1).
![Bash history](https://www.linux.com/sites/lcom/files/styles/rendered_file/public/commands_1.jpg?itok=2eqm9ii_ "Bash history")
Figure 1: Can you spot the mistake in one of my commands?[Used with permission][1]
The number of commands your Bash history holds is configured within the ~/.bashrc file. In that file, you’ll find two lines:
```
HISTSIZE=1000
HISTFILESIZE=2000
```
HISTSIZE is the maximum number of commands to remember on the history list, whereas HISTFILESIZE is the maximum number of lines contained in the history file.
Clearly, by default, Bash will retain 1000 commands in your history. That’s a lot. For some, this is considered an issue of security. If you’re concerned about that, you can shrink the number to whatever gives you the best ratio of security to practicality. If you don’t want Bash to remember your history, set HISTSIZE to 0.
If you make any changes to the ~/.bashrc file, make sure to log out and log back in (otherwise the changes won’t take effect).
### Apropos
This is the first of two tools that can be installed to assist you in recalling Linux commands. Apropos is able to search the Linux man pages to help you find the command you're looking for. Say, for instance, you don’t remember which firewall tool your distribution uses. You could type  _apropos “firewall” _ and the tool would return any related command (Figure 2).
![apropos](https://www.linux.com/sites/lcom/files/styles/rendered_file/public/commands_2.jpg?itok=MX5zHfet "apropos")
Figure 2: What is your firewall command?[Used with permission][2]
What if you needed a command to work with a directory, but had no idea what command was required? Type  _apropos “directory” _ to see every command that contains the word “directory” in its man page (Figure 3).
![apropos directory](https://www.linux.com/sites/lcom/files/styles/rendered_file/public/commands_3.jpg?itok=ALEsfP4q "apropos directory")
Figure 3: What was that tool you used on a directory?[Used with permission][3]
The apropos tool is installed, by default, on nearly every Linux distribution.
### Fish
There’s another tool that does a great job of helping you recall commands. Fish is a command line shell for Linux, Unix, and Mac OS that has a few nifty tricks up its sleeve:
* Autosuggestions
* VGA Color
* Full scriptability
* Web Based configuration
* Man Page Completions
* Syntax highlighting
* And more
The autosuggestions make fish a really helpful tool (especially when you can’t recall those commands).
As you might expect, fish isn’t installed by default. For Ubuntu (and its derivatives), you can install fish with the following commands:
```
sudo apt-add-repository ppa:fish-shell/release-2
sudo apt update
sudo apt install fish
```
For the likes of CentOS, fish can be installed like so. Add the repository with the commands:
```
sudo -s
cd /etc/yum.repos.d/
wget http://download.opensuse.org/repositories/shells:fish:release:2/CentOS_7/shells:fish:release:2.repo
```
Update the repository list with the commands:
```
yum repolist
yum update
```
Install fish with the command:
```
yum install fish
```
Using fish isn’t quite as intuitive as you might expect. Remember, fish is a shell, so you have to enter the shell before using the command. From your terminal, issue the command fish and you will find yourself in the newly install shell (Figure 4).
![fish shell](https://www.linux.com/sites/lcom/files/styles/rendered_file/public/commands_4.jpg?itok=8TBGVhVk "fish shell")
Figure 4: The fish interactive shell.[Used with permission][4]
Start typing a command and fish will automatically complete the command. If the suggested command is not the one you’re looking for, hit the Tab key on your keyboard for more suggestions. If it is the command you want, type the right arrow key on your keyboard to complete the command and then hit Enter to execute. When you’re done using fish, type exit to leave that shell.
Fish does quite a bit more, but with regards to helping you remember your commands, the autosuggestions will go a very long way.
### Keep learning
There are so many commands to learn on Linux. But don’t think you have to commit every single one of them to memory. Thanks to the Bash history and tools like apropos and fish, you won’t have to strain your memory much to recall the commands you need to get your job done.
--------------------------------------------------------------------------------
via: https://www.linux.com/learn/intro-to-linux/2017/10/3-tools-help-you-remember-linux-commands
作者：[JACK WALLEN ][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://www.linux.com/users/jlwallen
[1]:https://www.linux.com/licenses/category/used-permission
[2]:https://www.linux.com/licenses/category/used-permission
[3]:https://www.linux.com/licenses/category/used-permission
[4]:https://www.linux.com/licenses/category/used-permission
[5]:https://www.linux.com/licenses/category/used-permission
[6]:https://www.linux.com/files/images/commands1jpg
[7]:https://www.linux.com/files/images/commands2jpg
[8]:https://www.linux.com/files/images/commands3jpg
[9]:https://www.linux.com/files/images/commands4jpg
[10]:https://www.linux.com/files/images/commands-mainjpg
[11]:http://download.opensuse.org/repositories/shells:fish:release:2/CentOS_7/shells:fish:release:2.repo

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3 个帮你记住 Linux 命令的工具
============================================================
![apropos](https://www.linux.com/sites/lcom/files/styles/rendered_file/public/commands-main.jpg?itok=OESH_Evp "apropos")
The apropos tool, which is installed by default on nearly every Linux distribution, can help you find the command you need.[Used with permission][5]
Linux 桌面从开始的简陋走到现在的路很曲折。在我早期使用 Linux 的那段日子里，掌握命令行是最基本的 - 即使是桌面版。不过现在变了，很多人可能从没用过命令行。但对于 Linux 系统管理员来说，可不能这样。实际上，对于任何 Linux 管理员（不管是服务器还是桌面），命令行仍是必须的。从管理网络到系统安全，再到应用和系统设定 - 没有什么工具比命令行更强大。
但是，实际上。。。你可以在 Linux 系统里找到_非常多_命令。比如只看 _/usr/bin_ 目录，你就可以找到很多命令执行文件（你可以运行 _ls/usr/bin/ | wc -l_ 看一下你的系统里这个目录下到底有多少命令）。当然，它们并不全是针对用户的执行文件，但是可以让你感受下 Linux 命令数量。在我的 Elementary OS 系统里，目录 _/usr/bin_ 下有 2029 个可执行文件。尽管我只会用到其中的一小部分，我要怎么才能记住这一部分呢？
幸运的是，你可以使用一些工具和技巧，这样你就不用每天挣扎着去记忆这些命令了。我想和大家分享几个这样的小技巧，希望能让你们能稍微有效地使用命令行（顺便节省点脑力）。
我们从一个系统内置的工具开始介绍，然后再介绍两个可以安装的非常实用的程序。
### Bash 命令历史
不管你知不知道，Bash（最流行的 Linux shell）会保留你执行过的命令的历史。想实际操作下看看吗？有两种方式。打开终端窗口然后按向上方向键。你应该可以看到会有命令出现，一个接一个。一旦你找到了想用的命令，不用修改的话，可以直接按 Enter 键执行，或者修改后再按 Enter 键。
要重新执行（或修改一下再执行）之前运行过的命令，这是一个很好的方式。我经常用这个功能。它不仅仅让我不用去记忆一个命令的所有细节，而且可以不用一遍遍重复地输入同样的命令。
说到 Bash 的命令历史，如果你执行命令 _history_，你可以列出你过去执行过的命令列表（图 1）。
![Bash 命令历史](https://www.linux.com/sites/lcom/files/styles/rendered_file/public/commands_1.jpg?itok=2eqm9ii_ "Bash history")
图 1: 你能找到我敲的命令里的错误吗？[授权使用][1]
你的 Bash 命令历史保存的历史命令的数量可以在 ~/.bashrc 文件里设置。在这个文件里，你可以找到下面两行：
```
HISTSIZE=1000
HISTFILESIZE=2000
```
HISTSIZE 是命令历史列表里记录的命令的最大数量，而 HISTFILESIZE 是命令历史文件的最大行数。
is the maximum number of commands to remember on the history list, whereas HISTFILESIZE is the maximum number of lines contained in the history file.
显然，默认情况下，Bash 会记录你的 1000 条历史命令。这已经很多了。有时候，这也被认为是一个安全漏洞。如果你在意的话，你可以随意减小这个数值，在安全性和实用性之间平衡。如果你不希望 Bash 记录你的命令历史，可以将 HISTSIZE 设置为 0。
如果你修改了 ~/.bashrc 文件，记得要登出后再重新登录（否则改动不会生效）。
### Apropos
这是第一个我要介绍的工具，可以帮助你记忆 Linux 命令。Apropos 能够搜索 Linux 帮助文档来帮你找到你想要的命令。比如说，你不记得你用的发行版用的什么防火墙工具了。你可以输入 _apropos “firewall” _ ，然后这个工具会返回相关的命令（图 2）。
![apropos](https://www.linux.com/sites/lcom/files/styles/rendered_file/public/commands_2.jpg?itok=MX5zHfet "apropos")
图 2: 你用的什么防火墙？[授权使用][2]
再假如你需要一个操作目录的命令，但是完全不知道要用哪个呢？输入 _apropos “directory” _ 就可以列出在帮助文档里包含了字符“directory”的所有命令（图 3）。
![apropos directory](https://www.linux.com/sites/lcom/files/styles/rendered_file/public/commands_3.jpg?itok=ALEsfP4q "apropos directory")
图 3: 可以操作目录的工具有哪些呢？[授权使用][3]
apropos 工具在几乎所有 Linux 发行版里都会默认安装。
### Fish
还有另一个能帮助你记忆命令的很好的工具。Fish 是 Linux/Unix/Mac OS 的一个命令行 shell，有一些很好用的功能。
* 自动推荐
* VGA 颜色
* 完美的脚本支持
* 基于网页的配置
* 帮助文档自动填充
* 语法高亮
* 以及更多
自动推荐功能让 fish 非常方便（特别是你想不起来一些命令的时候）。
你可能觉得挺好，但是 fish 没有被默认安装。对于 Ubuntu（以及它的衍生版），你可以用下面的命令安装：
```
sudo apt-add-repository ppa:fish-shell/release-2
sudo apt update
sudo apt install fish
```
对于类 CentOS 系统，可以这样安装 fish。用下面的命令增加仓库：
```
sudo -s
cd /etc/yum.repos.d/
wget http://download.opensuse.org/repositories/shells:fish:release:2/CentOS_7/shells:fish:release:2.repo
```
用下面的命令更新仓库：
```
yum repolist
yum update
```
然后用下面的命令安装 fish：
```
yum install fish
```
fish 用起来可能没你想象的那么直观。记住，fish 是一个 shell，所以在使用命令之前你得先登录进去。在你的终端里，运行命令 fish 然后你就会看到自己已经打开了一个新的 shell（图 4）。
![fish shell](https://www.linux.com/sites/lcom/files/styles/rendered_file/public/commands_4.jpg?itok=8TBGVhVk "fish shell")
图 4: fish 的交互式 shell。[授权使用][4]
在开始输入命令的时候，fish 会自动补齐命令。如果推荐的命令不是你想要的，按下键盘的 Tab 键可以浏览更多选择。如果正好是你想要的，按下键盘的向右键补齐命令，然后按下 Enter 执行。在用完 fish 后，输入 exit 来退出 shell。
Fish 还可以做更多事情，但是这里只介绍用来帮助你记住命令，自动推荐功能足够了。
### 保持学习
Linux 上有太多的命令了。但你也不用记住所有命令。多亏有 Bash 命令历史以及像 apropos 和 fish 这样的工具，你不用消耗太多记忆来回忆那些帮你完成任务的命令。
--------------------------------------------------------------------------------
via: https://www.linux.com/learn/intro-to-linux/2017/10/3-tools-help-you-remember-linux-commands
作者：[JACK WALLEN ][a]
译者：[zpl1025](https://github.com/zpl1025)
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://www.linux.com/users/jlwallen
[1]:https://www.linux.com/licenses/category/used-permission
[2]:https://www.linux.com/licenses/category/used-permission
[3]:https://www.linux.com/licenses/category/used-permission
[4]:https://www.linux.com/licenses/category/used-permission
[5]:https://www.linux.com/licenses/category/used-permission
[6]:https://www.linux.com/files/images/commands1jpg
[7]:https://www.linux.com/files/images/commands2jpg
[8]:https://www.linux.com/files/images/commands3jpg
[9]:https://www.linux.com/files/images/commands4jpg
[10]:https://www.linux.com/files/images/commands-mainjpg
[11]:http://download.opensuse.org/repositories/shells:fish:release:2/CentOS_7/shells:fish:release:2.repo