Shell

Ref:

• profiles-and-rc-files
• https://shreevatsa.wordpress.com/2008/03/30/zshbash-startup-files-loading-order-bashrc-zshrc-etc/

Login Shell process

-  /etc/profile
  - /etc/profile.d/   # Add any custom profile configs inside here as .sh file

- .bash_profile       # Searches in the following order and the when the first
  .bash_login         # is found, executes it and stops. So if `.bash_profile`
  .profile            # is present, `.profile` is not executed.

- .bashrc             # Make sure it is called from one of the above.

- /etc/bashrc         # Usually no change here 
  [or] /etc/bash.bashrc  

Interactive Shell Process

- /etc/bashrc         #  
  [or] /etc/bash.bashrc  


- .bashrc            # Called directly without any profile being executed.

This shell doesn't look for any profile information at all, either system-wide or in the user directory. However, because an interactive shell is a "child" process of the login shell used to log in initially (either via GUI or SSH), it inherits all the profile information that initial login shell acquired.

Profiles

Profiles mainly are used to load environment variables. Since profiles are loaded by login shells, and login shells are the initial entry point into a system, that's the time when setting up the environment makes the most sense. One of the biggest environment variables is the PATH variable.

RC files

Used to set personal preferences for the command line. If you want a custom prompt, or prefer a specific color scheme, the bashrc system is where that would be set. Also aliases.

Recommendations

• ~/.bash_profile should be super-simple and just load .profile and .bashrc (in that order)
• ~/.profile has the stuff NOT specifically related to bash, such as environment variables (PATH and friends)
• ~/.bashrc has anything you'd want at an interactive command line. Command prompt, EDITOR variable, bash aliases for my use
• Anything that should be available to graphical applications OR to sh (or bash invoked as sh) MUST be in ~/.profile
• ~/.bashrc must not output anything
• Anything that should be available only to login shells should go in ~/.profile
• Ensure that ~/.bash_login does not exist.

---

For an “interactive non-login shell”, it reads .bashrc, but for an “interactive login shell” it reads from the first of .bash_profile, .bash_login and .profile (only). There is no sane reason why this should be so; it’s just historical. Follows in more detail.

+----------------+-----------+-----------+------+
|                |Interactive|Interactive|Script|
|                |login      |non-login  |      |
+----------------+-----------+-----------+------+
|/etc/profile    |   A       |           |      |
+----------------+-----------+-----------+------+
|/etc/bash.bashrc|           |    A      |      |
+----------------+-----------+-----------+------+
|~/.bashrc       |           |    B      |      |
+----------------+-----------+-----------+------+
|~/.bash_profile |   B1      |           |      |
+----------------+-----------+-----------+------+
|~/.bash_login   |   B2      |           |      |
+----------------+-----------+-----------+------+
|~/.profile      |   B3      |           |      |
+----------------+-----------+-----------+------+
|BASH_ENV        |           |           |  A   |
+----------------+-----------+-----------+------+
|                |           |           |      |
+----------------+-----------+-----------+------+
|                |           |           |      |
+----------------+-----------+-----------+------+
|~/.bash_logout  |    C      |           |      |
+----------------+-----------+-----------+------+

Reference: