Setting environment variables in Ubuntu

1, for a single user:
. BASHRC: Executes this file for each user running the bash shell. When the bash shell is opened, the file is read.
Open the. BASHRC in the home directory and add it to this file
Export path= "$PATH: Export path=" $PATH:/home/***/android-sdk-linux_86

/platform-tools/"
Make effective

source. BASHRC
2 , global settings:
/etc/profile is the environment variable for all users
Increase in/etc/profile
Export path= "$PATH:/home/***/android-sdk-linux_86/platform-tools/"
Complete Setup
Make effective

Source Profile

3 , System settings:
/etc/enviroment is the environment variable of the system
Export path= "$PATH:/home/***/android-sdk-linux_86/platform-tools/"
So when you configure a path to profile and enviroment, the default command cannot be used to open a new terminal. For example, the export path=****/android-sdk-linux_86 is set in profile and enviroment

After/platform-tools, the new terminal if not the source is still unable to use the ADB command, but if you set in the. BASHRC, the new terminal can be directly used by ADB.
Finally, if the same variable has different values in the user environment (/etc/profile) and the system environment (/etc/environment), then the user environment should prevail.

environment variables are and Shell closely related, the user logs on to the system and starts a Shell . It 's usually bashfor Linux , but it can be reset or switched to another Shell. For UNIX, it could be cshelll. Environment variables are set by Shell commands, and set environment variables can be used by all current users running programs. For bash , the Shell program can use variable names to access the corresponding environment variables through the export To set environment variables. This is illustrated by a few examples below.

1) etc/profile: This file sets the environment information for each user of the system , and the file is executed when the user logs on for the first time.
and collect the shell settings from the configuration file of the/ETC/PROFILE.D directory.
Note: Here we set the global variables that are available to all users.

2) /ETC/BASHRC: executes this file for each user running the bash shell. When the bash shell is opened, the file is read.

3) ~/.bash_profile: Each user can use this file to enter shell information dedicated to their own use, when a user logs on , the file executes only once ! By default, he sets some environment variables to execute the user's. bashrc file.
Note: ~ under LINUX is representative of HOME The of this variable.
under different LINUX operating systems, this file may be different, possibly ~/.bash _profile ~/.bash_login or ~/.profile one or more of these, if there are several, the order of execution is: ~/.bash_profile , ~/.bash_login , ~/.profile . For example, I'm using Ubuntu , and the default for my User folder is ~/.profile file. ,

4) ~/.BASHRC: This file contains bash information dedicated to your bash shell, which is read when you log in and every time you open a new shell.
(Note: This file is. Beginning, so it is hidden in the folder)
So how do we add our own defined environment variables?
Open the file with Notepad, and then write it in the last:
Xiaokang=kangkang
And then save it so that each time we open a new terminal, we have this variable in effect. Remember, if you have opened a terminal, and then you modify the file, then this terminal will not be effective. In general, the user is best to make changes here, but sometimes it will overwrite the parent variables, such as path is root set, but if you write in this file path=xx, then all of the future path is XX, so we should write in this file:
Path= $PATH: XX
This adds the original and your own. And note that the Linux system uses: Split to represent side by side, not windo;
3 and 4 are all in the user directory, their only difference is:. Bash_profile can only be started once when logging in. This 3 file does not seem to be in my Ubuntu.

5) ~/.bash_logout: Executes the file each time it exits the system (exiting the bash shell).
In addition, the variables set in/etc/profile (global) can be applied to any user, while the variables set in ~/.BASHRC, etc. (local) only inherit variables from/etc/profile, they are "parent-child \" relationships.

6) ~/.bash_profile is interactive, login way into bash run
~/.BASHRC is an interactive non-login way into bash run
Usually the two settings are roughly the same, so the former usually calls the latter.

OK, let's summarize how they do it:
When you log in and the shell is bash, bash first executes the command in the/etc/profile file (if the file exists), and then it looks for the ~/.bash_profile,~/.bash_login or ~/.profile file sequentially, and executes the command found in the first readable file. When login bash exits, it executes the commands in the ~/.bash_logout file.
When you start an interactive bash, it executes the commands in the ~/.BASHRC file (if the file exists and is readable). When you start non-interactively to run a shell script, bash looks for the BASH_ENV environment variable to determine the name of the execution file.

When you first log in to Linux, start the/etc/profile file, and then start the user directory

~/.bash_profile; ~/.bash_login or ~/.profile file.

One ( depending on the different Linux operating systems, the naming is not the same!!!!!!!!!! In my Ubuntu only ~/.profile),

The order of execution is: ~/.bash_profile, ~/.bash_login, ~/.profile.
If the ~/.bash_profile file exists, the ~/.BASHRC file is typically executed.

Because the following code is commonly found in the ~/.bash_profile file:
If [-f ~/.BASHRC]; Then
. ./BASHRC
Fi
In ~/.BASHRC, the following code is generally available:
if [-F/ETC/BASHRC]; Then
. /bashrc
Fi
Therefore, ~/.BASHRC will call the/ETC/BASHRC file. Finally, when you exit the shell, the ~/.bash_logout file is also executed.
Order of execution:/etc/profile---(~/.bash_profile | ~/.bash_login | ~/.profile), ~/.BASHRC,/ETC/BASHRC, ~/.bash_lo Gout
The use of various environment variable settings files such as/etc/profile and/etc/environment

First add the export LANG=ZH_CN to/etc/profile, exit the system to log in again, login prompt display in English.
Delete the export lang=zh_cn in/etc/profile, add LNAG=ZH_CN to/etc/environment, exit the system to log in again, sign in prompt to display Chinese.
The user environment is established by always executing/etc/profile and then reading the/etc/environment. Why is it as different as the above?
The/etc/environment should be executed first and then executed/etc/profile.
/etc/environment is the environment that sets up the entire system, and/etc/profile is the environment for setting up all users, regardless of the logged-on user, which is related to the logged-on user.
The execution of the system application can be irrelevant to the user environment, but it is related to the system environment, so when you log in, you see the prompt information, such as date, time information display format is related to the system environment Lang, default Lang=en_us, if the system environment LANG=ZH_CN, The message is in Chinese, otherwise it is in English.

For a user's shell initialization, the/etc/profile is executed first, and then the file/etc/environment is read. The/etc/environment is performed first for the entire system. Do you understand that correctly?
/etc/enviroment--/etc/profile-$HOME/.profile--$HOME/.env (if present)
/etc/profile is the environment variable for all users
/etc/enviroment is the environment variable of the system
The order in which the shell reads the system when logging in should be
/etc/profile->/etc/enviroment-$HOME/.profile-$HOME/.env
The reason should be the difference between the user environment and the system environment described by JTW.

Setting environment variables in Ubuntu