Variables in Linux

The variables in Linux are divided into

Local variables, environment variables, local variables, positional variables, special variables

Local variables: Valid for the current shell process only, effective immediately

Usage: variable name = value

Reference: ${variable name}, greater than number can be omitted

Cases

[Email protected] ~]# Name=jerry[[email protected] ~]# echo $namejerry

Environment variables:

1. Valid for all child shells of the current shell and current shell, effective immediately, logout is invalid

Usage: Export Variable name = value

Cancel: unset variable name

Cases

[[email protected] ~]# export Name=andy[[email protected] ~]# bash[[email protected] ~]# echo $nameandy [[email protected] ~]# Exitexit

2, valid for all shells, write to file, command load or re-login takes effect

File All directories: Interactive/etc/profile,/etc/profile.d/*.sh or ~/.bash_profile, non-interactive/ETC/BASHRC, ~/.BASHRC

After writing, use: . File name or source file name to import, or you can log in again

There are many environment variables in bash, which are usually denoted by the command: Set,export, printenv,env to query

The following is a sequence of configuration file access for both interactive and non-interactive logon types

Interactive:/etc/profile-->/etc/profile.d/*.sh-->~/.bash_profile-->~/.bashrc--> ETC/BASHRC

Non-interactive: ~/.bashrc-->/etc/bashrc--> etc/profile.d/*.sh

Local variables

Variables in a function

Position variable: The first parameter that represents a reference

$, $2...${10} double-digit to use greater than sign

Special variables

$?: Execution status of last command 0 indicates success, greater than 1 means unsuccessful and corresponding error code

$#: Number of parameters

$* or [email protected]: all parameters

Variables in Linux