Lesson 4 of my Longco operation and maintenance (1)
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
