Set environment variables
1. Execute export directly in the shell
After setting, it is only valid for the current terminal, other terminals cannot obtain this variable
2. Edit the .bash_profile file in the user's home directory, the variables defined in this file are only valid for the current user
add at the end
After saving, it is still not available in the current shell, you need to make the modification take effect, execute
After the execution, the newly set variable can be obtained in the current shell, but still cannot be obtained in other shells. You need to execute the source command in another shell. The best way is to log out and log in or restart.
3. Edit the /etc/profile file, the variables defined in this file are valid for all users
add at the end
After saving, it is still not available in the current shell. You need to make the modification take effect, and 
you can obtain the newly set variables in the current shell by executing it, but it is still unavailable in other shells. You need to execute the source command in another shell. , the best way is to log out and log in or restart,