Linux environment variables

1. Use the ENV command to display all environment variables

　　$ env

hostname=redbooks.safe.org

Pvm_rsh=/usr/bin/rsh

Shell=/bin/bash

Term=xterm

histsize=1000

...

2. Use the SET command to display all locally defined shell variables

$ set

3. Use the unset command to clear environment variables

Set sets the value of an environment variable. Clear the value of the environment variable with the unset command. If no value is specified, the value of the variable is set to NULL. Examples are as follows:

$ export test= "TEST ..." #增加一个环境变量TEST

$ env|grep Test #此命令有输入, proving that the environment variable test already exists

Test=test ...

　$ unset $TEST #删除环境变量TEST

$ env|grep Test #此命令没有输出, proving that the environment variable test already exists

4. Use the echo command to view a single environment variable. For example:

　Echo $PATH

5. Common environment variables

PATH determines to which directories the shell will look for commands or programs

Home Current User Home directory

Histsize Number of historical records

LOGNAME The current user's login name

HOSTNAME refers to the name of the host

Shell Current User shell type

Languge language-related environment variables, multiple languages can modify this environment variable

Mail storage directory for the current user of mail

PS1 basic prompt, for root user Yes #, for normal user is $

6. Set a new environment variable Hello

$ export hello= "hello!"

$ echo $HELLO

Hello!

Linux environment variables