Use of shell (1) variables in Linux, linuxshell

Use of shell (1) variables in Linux, linuxshell

One Variable

Echo $ a: output variable a. If it does not exist, a variable a is created.

Unset a: Cancel variable

1.1 environment variables:

Env: View descriptions of environment variables and common variables

HOME: Your main folder

HISTSIZE: Number of historical commands that can be recorded by the System

PATH: PATH of the execution file query

LANG: modifiable language family

Set: view all variables, including environment variables and custom Variables

PS1: Command Prompt

Export: You can convert custom variables to environment variables.

Language: locale

Keyboard reading, array, and Declaration of 1.2 Variables

Read: read variables from keyboard input

For example, read-p "please input your name:"-t 30 name (after the command is executed, please input your name:) your input value will be included in the variable name, if this parameter is not entered for more than 30 seconds, the system will be disqualified

-P: Followed by a prompt

-T: the number of seconds that can be followed.

Declare/typeset: declare the type of the Variable

Declare [-aixr] variable name

-A: defines variables of the array type.

-I: defines integer variables.

-X: Change the variable after the parameter to the environment variable.

-R: Set the variable to read-only.

Note: The default variable type is "string"

Array: array variable type

Delete, replace, and replace variable content

Variable setting method

$ {Variable # keyword} if the variable content matches the keyword from the beginning, the minimum data that matches the keyword is deleted.

$ {Variable ## keyword} if the variable content matches the keyword from the beginning, the longest matching data will be deleted.

$ {Variable % keyword} if the variable content matches the keyword from the forward data, the minimum data that matches the keyword is deleted.

$ {Variable % keyword} if the variable content matches the keyword from the end to the forward data, the longest matching data is deleted.

$ (Variable/old string/New String) if the variable content matches the old string, the first old string will be replaced by the new string

$ {Variable // old string/new string} if the variable content matches the old string, all old strings will be replaced by the new string