【Shell脚本基础系列-1】入门 Getting started

目录

1. 入门
2. if-else分支和for/while循环
3. 环境变量
4. 函数的使用
5. 文件读写操作
6. 睡眠
7. 进程状态监测
8. 用户交互

Getting started

Create an empty file Using touch

1. Primary function of touch: To modify a timestamp

2. Common utility:
   To create a file if it does not already exist

   $ touch hello_world.sh 
   

Chmod

$ bash hello_world.sh
$ ./hello_world.sh (Error: permission denied)

By default, files are not executable.

$ chmod 755 hello_world.sh 
$ ./hello_world.sh (Fine!)

$ hello_world.sh (Error: command not found)

• Why ./

  Linux systems look for command on the path, not the current directory. ./ tells the system don’t bother with the path, look at the current directory.

The Shebang

Tells which command processor should handle this script Must be the first line, or will be ignored as a comment

• For bash
  • #!/usr/bin/env bash (<- recommended)
  • #!/bin/bash
• For python
  • #!/usr/bin/env python
• For java script
  • #!/usr/bin/env node

Variables

#!/usr/bin/env bash

NAME="Bob Roberts"
COLOR=Blue

echo Hi $NAME, your favorite color is $COLOR.

Semantics

• Must begin with a letter or an underscore (not a number)
• Are case sensitive (usually all uppercase)
• No spaces either side of the equal sign (double quote sign needed if spaces are needed in the value)

Parameters

Make it possible to interact with the user

#!/usr/bin/env bash

USER_NAME=$1
echo Hello $USER_NAME
echo $(date)  # out date and time
echo $(pwd)   # print working directory

exit 0

Check if the execution is successful: print the last (most recent) exit code that the system received

echo $?  

• $0: the name of the script, the path is included
• $1: the 1st parameter
• $2: the 2nd parameter
• ${10}: the 10th parameter (use of curly braces required for above 9.)

References

LinkedIn Learning: https://www.linkedin.com/learning/learning-linux-shell-scripting-2018