What are the Linux environment variables?

Linux environment variables include: 1. HOME, the user’s home directory (also called home directory); 2. SHELL, the name of the Shell interpreter used by the user; 3. PATH, which defines the command line interpreter to search for user execution The path of the command; 4. EDITOR, the user's default text interpreter; 5. RANDOM, generates a random number; 6. LANG, the system language and language family name; 7. HISTSIZE, the number of historical command records output; 8. HISTFILESIZE; 9. PS1; 10. MAIL.

#The operating environment of this tutorial: linux7.3 system, Dell G3 computer.

What are environment variables

Variables are data types used by computer systems to store variable values. We can extract them directly through the variable name. to the corresponding variable value.

In Linux systems, environment variables are used to define some parameters of the system's operating environment, such as each user's different home directory (HOME), mail storage location (MAIL), etc.

It is worth mentioning that the names of environment variables in Linux systems are generally in uppercase letters, which is a convention.

Detailed explanation of Linux environment variables

##View syntax

env

View Single environment variable value

echo $ENVNAME

Set the value of the environment variable

ENVNAME=value

Environment variable list

Environment variable nameFunctionHOMEThe user’s home directory (also called home directory )SHELLThe name of the Shell interpreter used by the userPATHDefine the command line interpretation The path where the browser searches for the user's command executionEDITORUser's default text interpreterRANDOMGenerate a random numberLANGSystem language and language nameHISTSIZEOutput Number of historical command recordsHISTFILESIZENumber of saved historical command recordsPS1 Bash interpreter promptMAILMail saving path

Description

Using the env command, we can view all the environment variables of the current system. Using the echo command, we can view the value of a single environment variable. We can directly use the form of "environment variable name = value" to set the value of the environment variable. .

Expand knowledge

Linux, as a multi-user and multi-tasking operating system, can provide independent and suitable work operations for each user. Environment, therefore, the same environment variable will have different values ​​depending on the user's identity.

For example, use the following command to view the values ​​of the HOME variable under different user identities:

[root@localhost ~]# echo $HOME
/root
[root@localhost ~]# su - user1  <--切换到 user1 用户身份
[user1@localhost ~]$ echo $HOME
/home/user1

The su command here can temporarily switch user identities. The specific usage of this command will be in Detailed introduction will be provided in subsequent chapters.

In fact, environment variables are composed of fixed variable names and variable values ​​set by the user or system. We can create environment variables by ourselves to meet work needs. For example, to set an environment variable named WORKDIR to facilitate users to enter a deeper directory more easily, the execution command is as follows:

[root@localhost ~]# mkdir /home/work1
[root@localhost ~]# WORKDIR=/home/work1
[root@localhost ~]# cd $WORKDIR
[root@localhost work1]# pwd
/home/work1

However, such an environment variable is not global and has limited scope. , which cannot be used by other users by default. If needed for work, you can use the export command to promote it to a global environment variable so that other users can use it:

[root@localhost work1]# su user1  <-- 切换到 user1，发现无法使用 WORKDIR 自定义变量
[user1@localhost ~]$ cd $WORKDIR
[user1@localhost ~]$ echo $WORKDIR

[user1@localhost ~]$ exit <--退出user1身份
[root@localhost work1]# export WORKDIR
[root@localhost work1]# su user1
[user1@localhost ~]$ cd $WORKDIR
[user1@localhost work1]$ pwd
/home/work1

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