# Shell

1. 书籍分享：

   introduction-to-bash-scripting

   <https://github.com/bobbyiliev/introduction-to-bash-scripting>

   书中介绍了 Shell 的基本语法特性，并用多个案例带你实战。

   虽然此书一共才122页，但内容很全面，由浅入深。值得阅读。
2. 知识分享：

   chmod: 改变文件权限

   文件权限有两种设置方法，一种是数字权限，一种是符号权限。

   Linux 文件的基本权限就有九个，分别是 **user/group/others(拥有者/组/其他)** 三种身份各有自己的 **read/write/execute** 权限。

   1. 符号权限方式：

      `chmod [-R] [u,g,o] [+,-,=] [文件或目录]`

      `-R`: 目录下的所有文件都会变更

      user/group/others(拥有者/组/其他) 分别对应的缩写为 u,g,o

      `+` 代表增加权限，`-` 代表删除权限，`=`代表设置权限

      例：`chmod u=rwx,g=rx,o=r 文件名`
   2. 数字改变权限方式

      各权限的分数对照表

      * r:4
      * w:2
      * x:1

      rwx = 4 + 2 + 1 = 7

      wx = 2 + 1 = 3 rx = 4 + 1 = 5

      rw = 4 + 2 = 6

      `chmod [-R] xyz 文件或目录`

      `-R`: 目录下的所有文件都会变更

      xyz : 就是刚刚提到的数字类型的权限属性，为 rwx 属性数值的相加。

      例：`chmod 777 .bashrc` => -rwxrwxrwx
   3. ![image-20201202194022778](/files/-MPZDbnlrUTtH6orISd0)

      我就简单多了

      ![image-20201202194044134](/files/-MPZDbnm6HRoxBQKzy9y)
   4. 快餐文分享:

      Defensive BASH Programming

      <https://kfirlavi.herokuapp.com/blog/2012/11/14/defensive-bash-programming/> 摘要: Here is my Katas for creating BASH programs that work. Nothing is new here, but from my experience pepole like to abuse BASH, forget computer science and create a [Big ball of mud](http://en.wikipedia.org/wiki/Big_ball_of_mud) from their programs. Here I provide methods to defend your programs from braking, and keep the code tidy and clean.

      由于 Shell 的糟糕设计, 作者提出了 防御性编程规范...
3. Shell的魅力

   ![image-20210206215911726](/files/-MSrkk-wwly3r-B7fD86)

   A: jq 不会是 jquery 吧。？

   B: 不是 Go写的 查询 json 的一个知名工具
4. sudo=速冻 cd=吃的 ls=零食 ps=披萨 ssh=熟食 scp=水产品
5. alias please=sudo


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://thinking.simonaking.com/tags/pl/shell.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.