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Variables for the bash feature:

Variable name: a continuous memory space name.

Variable value: the data stored in the variable name.

Naming rules:

1. Can only start with a letter or "_", cannot use a number, and can be followed by any letter, number, and underscore

two。 Strict distinction between case and case

3. See the name and know the meaning

4. Writing rules:

1) all uppercase

2) Hump style

5. Cannot be the same as a known variable name

Species:

Global variable (environment variable): acts on the entire shell process, including its child shell

Local variable: only acts on the shell of the current login, excluding the child shell

Local variable: acts only as a moneyable program segment, generally used for functions

Default global variables: $?, $#, $*, $@, $$,.

$?: expand the status of the last executed command

$#: position parameters, expressed in decimal system

$*: expand all parameters

$@

$

$0: expand the file name of the shell or shell script

$LANG: storage language

$PS1: command prompt

Use of variables:

Declare a local variable: VARNAME=VALUE

Undo variable: unset VARNAME

Declare the environment variable: export VARNAME

Export VARNAME=VALUE

Declare

-a: declare an indexed array

-A: declare an associative array

-I: declare integer variables

-l: declare variables and convert characters in variable values to lowercase letters

-u: declare variables and convert characters in variable values to uppercase letters

-x: declare variables and make them environment variables everywhere

-r: declare a variable as read-only

View environment variables: export, set, env,

Declare a local variable: local VARNAME=VALUE

To take effect permanently, you need to change the configuration file:

Common configuration files: / etc/bashrc, / etc/profile

Private configuration files: ~ / .bashrc, ~ / .bash_profile

Reload the configuration file: source .bashrc,. .bashrc

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