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[#]: collector: (lujun9972)
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[#]: translator: (HankChow)
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[#]: reviewer: ( )
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[#]: publisher: ( )
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[#]: url: ( )
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[#]: subject: (Aliases: DIY Shell Commands)
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[#]: via: (https://www.linux.com/blog/learn/2018/12/aliases-diy-shell-commands)
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[#]: author: (Paul Brown https://www.linux.com/users/bro66)
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Aliases: DIY Shell Commands
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======
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Aliases, in the context of the Linux shell, are **commands you build yourself** by packing them with combinations of other instructions that are too long or too hard to remember.
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You create an alias by using the word `alias`, then the name of the command you want to create, an equal sign (`=`), and then the Bash command(s) you want your alias to run. For example, `ls` in its base form does not colorize its output, making it difficult to distinguish between directories, files, and links. You can build a new command that shows colors by making an alias like this:
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```
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alias lc='ls --color=auto'
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```
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where `lc` is the name you have picked for your new command. When creating aliases, be sure to check that the name you picked isn't already in use, or you may override an existing command. In this case, `lc` stands for "list (with) color". Notice there is no space in front of or behind the `=`. Finally, you have the regular Bash command(s) you want to run when `lc` is executed. In this case, the `ls` command with the `--color` option.
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After defining your alias, every time you type `lc`, the contents of the current directory will be shown in color.
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But, you may think, "my `ls` command already lists files in different colors!" That is because most Linux distros come with some aliases already set up for you.
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### Aliases you (probably) already have
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Indeed, you can use the `alias` instruction without any options to see what aliases you already have. These will vary by distro, but some typical preset aliases are:
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* `alias ls='ls --color=auto'`: You already saw this one above. The `auto` modifier of the `--color` option tells `ls` to use color when standard output is connected to a terminal. That is, the output of `ls` is going to show up in a terminal window or a text screen, instead of, say, being piped to a file. Other alternatives for `--color` are `always` and `never`.
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* `alias cp='cp -i'`: The `-i` option stands for _interactive_. Sometimes, when you use `cp` you may inadvertently overwrite an existing file. By using the `-i`, `cp` will ask you before clobbering anything.
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* `alias free='free -m'`: Using `-m` with `free`you can see how much free memory you have and how much your applications are using in megabytes instead of the default bytes. This makes the output of `free` easier to read for a human.
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There may be more (or less, or even none), but regardless of what your distribution comes with, you can always use the base form (vs. the aliased form) of a command with the `\` modifier. For example:
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```
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\free
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```
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will execute `free` without the `-m` option, and
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```
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\ls
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```
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will execute `ls` without the `--color=auto` option.
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If you want to get rid or modify the preset aliases forever, note that they live in the global _.bashrc_ file which hangs out in [our old haunt, the _/etc/skel_ directory][1].
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### Aliases for muscle memory
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Distro designers try their best to predict which aliases are going to be useful for you. But every user is different and comes from a different background. If you are new to GNU+Linux, it may be because you are coming from another system, and the basic commands vary from shell to shell. If you come from a Windows/MS-DOS background, you may want to define an alias like
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```
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alias dir='ls'
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```
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to list files or directories.
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Likewise,
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```
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alias copy='cp'
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alias move='mv'
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```
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may also come in handy, at least until you get used to Linux's new lexicon.
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The other problem occurs when mistakes become ingrained in your muscle memory, so you always mistype some words the same way. I, for instance, have great difficulty typing _admnis-_... _adminsi-_... _A-D-M-I-N-I-S-T-R-A-T-I-ON_ ( _phew!_ ) at speed. That is why some users create aliases like
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```
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alias sl='ls'
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```
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and
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```
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alias gerp='echo "You did it *again*!"; grep'
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```
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Although we haven't formally introduced `grep` yet, in its most basic form, it looks for a string of characters in a file or a set of files. It's one of those commands that you will tend to use A LOT once you get to grips with it, as those ingrained mistyping habits that force you to type the instruction twice every time get annoying really quickly.
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Another thing to note in the `gerp` example is that it is not a single instruction, but two. The first one (`echo "You did it *again*!"`) prints out a message reminding you that you misspelled the grep command, then there is a semicolon (`;`) that separates one instruction from the other. Finally, you've got the second command (`grep`) that does the actual grepping.
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Using `gerp` on my system to search for the lines containing the word " _alias_ " in _/etc/skel/.bashrc_ , the output looks like this:
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```
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$ gerp -R alias /etc/skel/.bashrc
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You did it *again*!
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alias ls='ls --color=auto'
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alias grep='grep --colour=auto'
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alias egrep='egrep --colour=auto'
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alias fgrep='fgrep --colour=auto'
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alias cp="cp -i"
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alias df='df -h'
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alias free='free -m'
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alias np='nano -w PKGBUILD'
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alias more=less
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shopt -s expand_aliases
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```
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Running commands sequentially as part of an alias, or, even better, chaining commands so that one command can use the results coughed up by another, is getting us perilously close to Bash scripting. This has been in the making of this series for quite some time, and we'll start covering it in the very next article.
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For the time being, if you want to get rid of an alias you temporarily set up in a running terminal, use the `unalias` command:
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```
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unalias gerp
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```
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If you want to make your aliases permanent, you can drop them into the _.bashrc_ file you have in your home directory. This is the same thing we did with custom environment variables in [last week's article][2].
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See you next time!
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--------------------------------------------------------------------------------
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via: https://www.linux.com/blog/learn/2018/12/aliases-diy-shell-commands
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作者：[Paul Brown][a]
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选题：[lujun9972][b]
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译者：[译者ID](https://github.com/译者ID)
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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) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]: https://www.linux.com/users/bro66
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[b]: https://github.com/lujun9972
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[1]: https://www.linux.com/learn/intro-to-linux/2018/7/users-groups-and-other-linux-beasts
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[2]: https://www.linux.com/blog/learn/2018/12/bash-variables-environmental-and-otherwise
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命令别名：定义自己的命令
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======
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<ruby>命令别名<rt>Alias</rt></ruby>在 Linux shell 中指的是将一些太长或者太难记的多个命令组合起来，成为一个由用户自定义构建的命令。
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可以通过 `alias` 命令来创建命令别名。在 `alias` 后面跟上想要创建的别名名称、一个等号（`=`），以及希望使用这个别名来执行的命令，这样一个命令别名就创建好了。举个例子，`ls` 命令在默认情况下是不会对输出的内容进行着色的，这样就不能让用户一眼分辨出目录、文件和连接了。对此，可以创建这样一个命令别名，在输出目录内容的时候为输出内容着色：
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```
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alias lc='ls --color=auto'
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```
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其中 `lc` 是自定义的命令别名，代表“list with color”的意思。在创建命令别名的时候，需要先确认使用的别名是不是已经有对应的命令了，如果有的话，原本的命令就会被覆盖掉了。注意，定义命令别名的时候，`=` 两端是没有空格的。当运行 `lc` 的时候，就相当于执行了 `ls --color` 命令。
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此后，执行 `lc` 列出目录内容的时候，就会输出带有着色的内容了。
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你可能会发现你在执行 `ls` 的时候，本来就是输出带有着色的内容。那是因为大部分 Linux 发行版都已经将 `ls` 设定为带有着色的命令别名了。
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### 可以直接使用的命令别名
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实际上，执行不带任何内容的 `alias` 命令就可以看到当前已经设定的所有命令别名。对于不同的发行版，包含的命令别名不尽相同，但普遍都会有以下这些命令别名：
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* `alias ls='ls --color=auto'`：这个命令别名在前面已经提到过了。`--color=auto` 参数会让 `ls` 命令在通过标准输出在终端中显示内容时进行着色，而其它情况（例如通过管道输出到文件）下则不进行着色。`--color` 这个参数还可以设置为 `always` 或`never`。
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* `alias cp='cp -i'`：`-i` 参数代表“<ruby>交互<rt>interactive</rt></ruby>”。在使用 `cp` 命令复制文件的时候，可能会无意中覆盖现有的文件，在使用了 `-i` 参数之后，`cp` 命令会在一些关键操作前向用户发出询问。
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* `alias free='free -m'`：在 `free` 命令后面加上 `-m` 参数，就可以将输出的内存信息以 MiB 这个更方面阅读和计算的单位输出，而不是默认的 Byte 单位。
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你使用的发行版自带的命令别名可能多多少少和上面有些差别。但你都可以在命令前面加上 `\` 修饰符来使用命令的最基本形式。例如：
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```
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\free
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```
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就是直接执行 `free`，而不是 `free -m`。还有：
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```
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\ls
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```
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执行的就是不带有`--color=auto` 参数的 `ls`。
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如果想要持久地保存命令别名，可以在 `.bashrc` 文件中进行修改。
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### 使用命令别名纠正错误
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各种发行版的设计者都会尽量设置用户可能需要用到的命令别名。但是不同的用户的习惯各不相同，一些用户可能刚从其它操作系统迁移到 Linux，而不同操作系统的基本命令又因 shell 而异。因此，对于刚从 Windows/MS-DOS 系统迁移到 Linux 系统的用户，不妨使用
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```
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alias dir='ls'
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```
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这个命令别名来列出目录内容。
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类似地，
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```
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alias copy='cp'
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alias move='mv'
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```
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也可以在尚未完全熟悉 Linux 的时候用得顺手。
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还有一种情况，就是在经常出现输入错误的场合中做出容错，例如 Administration 这个单词就很难快速正确地输入，因此很多用户都会设置
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```
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alias sl='ls'
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```
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以及
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```
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alias gerp='echo "You did it *again*!"; grep'
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```
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`grep` 命令最基本的用途就是在文件中查找字符串，在熟悉这个命令之后，它一定是最常用的命令之一，因此输入错误导致不得不重输命令就很令人抓狂。
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在上面 `gerp` 的例子中，包含的不只是一条命令，而是两条。第一条命令 `echo "You did it *again*!"` 输出了一条提醒用户拼写错误的消息，然后使用分号（`；`）把两条命令隔开，再往后才是 `grep` 这一条正确的命令。
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在我的系统上使用 `gerp` 来搜索 `/etc/skel/.bashrc` 中包含“alias”这个单词的行，就会输出以下内容：
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```
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$ gerp -R alias /etc/skel/.bashrc
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You did it *again*!
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alias ls='ls --color=auto'
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alias grep='grep --colour=auto'
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alias egrep='egrep --colour=auto'
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alias fgrep='fgrep --colour=auto'
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alias cp="cp -i"
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alias df='df -h'
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alias free='free -m'
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alias np='nano -w PKGBUILD'
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alias more=less
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shopt -s expand_aliases
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```
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在命令别名中以固定的顺序执行多个命令，甚至更进一步，把多个命令串连起来，让后面的命令可以使用到前面的命令的执行结果。这样的做法已经非常接近 bash 脚本了。这篇文章已经接近尾声，我们将在下一篇文章中详细介绍。
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如果想要删除在终端中临时设置的别名，可以使用 `unalias` 命令。
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```
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unalias gerp
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```
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如果想要持久保存命令别名，可以将命令别名放在用户主目录的 `.bashrc` 文件中，具体的方法在[上一篇文章][2]中已经介绍过。
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--------------------------------------------------------------------------------
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via: https://www.linux.com/blog/learn/2018/12/aliases-diy-shell-commands
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作者：[Paul Brown][a]
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选题：[lujun9972][b]
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译者：[HankChow](https://github.com/HankChow)
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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) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]: https://www.linux.com/users/bro66
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[b]: https://github.com/lujun9972
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[1]: https://www.linux.com/learn/intro-to-linux/2018/7/users-groups-and-other-linux-beasts
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[2]: https://www.linux.com/blog/learn/2018/12/bash-variables-environmental-and-otherwise
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