Detailed explanation of .bash_profile file in Linux system

1. Environment variable $PATH:

Linux is a多用戶操作系統, and each user has his or her own dedicated operating environment. The environment used by the user is defined by a series of variables, which are called環境變量. System environment variables are usually in大寫.

Each user can modify their own environment variables as needed to meet their own usage requirements. Common environment variables are as follows:

In Shell , the dollar sign $ is used to reference environment variables, and the echo command can be used to view the value of a specific environment variable.

For example, to view the value of PATH:

 echo $PATH 

You can view all the system environment variable settings by using the env or printenv command. The following shows the result of the env command (partial):

 TERM=xterm
SHELL=/bin/bash
USER=leo
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games
HOME=/home/leo
LANGUAGE=zh_CN:zh:en_US:en
LOGNAME=leo

2. Modify environment variables:

Logged-in users can modify and set environment variables as needed. To modify environment variables in Linux,既可以在終端通過Shell 命令修改，也可以通過修改系統的配置文件來進行.

2.1 Modify the system configuration file (recommended)

By modifying the system configuration file, you can achieve the purpose of永久改變the environment variables. After modifying a configuration file, run the file in Shell to make the new settings take effect, or log in again to use the new variables.

Running files can be operated in the same way as source 文件, for example:

 source ~/.bash_profile

Usually modify全局配置文件/etc/profile or用戶配置文件~/.bashrc (some distributions are ~/.bash_profile ) file:

For example:

 PATH=$PATH:$HOME/bin

Specific insights are as follows:

The code $HOME is an environment variable, which represents the home folder of the currently logged in user. (It's the one in the home directory)

The code $HOME/bin refers to the bin subdirectory under the home folder, which represents the internal subdirectory of the folder. (Note that it is not the root directory)

PATH=$PATH:$HOME/bin This code sets the PATH environment variable. Use the equal sign to set the environment variable, : the colon is a separator. When adding environment variables on Windows ; separate them with a semicolon and append them afterwards. Similarly, on Mac, use : to separate the characters and append them.

$PATH:$HOME/bin means that while retaining the original $PATH environment variable, $HOME/bin is added as the new $PATH environment variable. There are many variables in computers, which are mainly used in the management of system files.

Note: The path environment variable is PATH, but add a $ in front when quoting it, that is, $PATH

2.2 Temporary settings

Setting environment variables through Shell 命令is often used to temporarily set environment variables. Once the current terminal is closed or a new terminal is opened, the set environment variables will be lost. You can directly use the equal sign (=) to assign a value to a variable, or use the export command to assign a value to a variable. Usage:

 variable = $variable: add variable value #method 1export variable = $variable: add variable value #method 2

For example:

picture

The newly added variable value can be placed at the end of the original variable value (variable: new variable value), at the beginning of the original variable value (new variable value: variable: new variable value), or at the beginning of the original variable value (new variable value: variable: new variable value).

3. Purpose of bash_profile

In .bash_profile, it is often used to configure environment variables and some user-defined aliases, etc.

Summarize

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