The bash shell uses several startup files. Bash uses more than one startup file. Bash users tend to have trouble determining which file they should use for new, automatically executed commands.
Here's a quick review of the startup files that bash can use, followed by a discussion of when these startup files are important. Here, tilde (~) refers to your home directory.
The /etc/profile is the main startup file for bash. It is located in the /etc directory, to be used for commands all users need. In contrast, a user's home directory contains one or more of the following bash startup files, which contain commands that apply only to the current user's bash session: ~/.bash_profile, ~/.bash_login, ~/.profile, ~/bash_rc, and ~/.bash_logout.
To understand how bash employs the various user startup files, you must understand the difference between a login shell and a nonlogin shell. A login shell is created when you log in to your Linux account. A nonlogin shell is created when you launch an additional bash shell within your user session, as you do when you open a terminal window in X or when you run additional screens.
When you start a login shell, bash consults the following files in the specified order:
When you start a nonlogin shell, bash consults only one startup file, ~/bash.rc.
The shells may differ because login and nonlogin shells use different startup files. Most Linux distributions contain an automatically generated ~./bash_profile that contains a script that automatically executes the commands placed in ~/bash_rc. This script ensures that the login shell will be configured like the nonlogin shell.
You can write your own scripts here to run processes everytime you run the shell. Although this script is useful, a full understanding of the way bash works with startup files is needed if you wish to understand just where you should add commands to a bash startup file.
To add a command that is automatically executed when any user begins a login shell, add the command to /etc/profile. You'll need to switch to superuser status to edit this file.
To add a command that is executed when you start a login shell in your own user account, use ~/bash.profile for commands that must be executed before commands contained in ~/.bash_login or ~/profile. Use ~/.profile for commands that must be executed only after the shell executes the commands found in ~/.bash.profile and ~/bash_login.
To add a command that is executed when you start a nonlogin shell, use ~/.bashrc.
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