The confusing Bash configuration files

This blog is mostly a reminder for my future self, because I always end up forgetting this.

Bash has a bunch of configuration files it parsers through when you fire it up.

Bash reads them in this order (on Fedora, and I suppose RHEL and derivatives too) if invoked as an interactive login shell (i.e. when you log into the system on the console, or through SSH):

• /etc/profile (if it exists)
• ~/.bash_profile (if it exists)
• ~/.bash_login (if it exists, and ~/.bash_profile does not exist)
• ~/.profile (if it exists, and if the above two files do not)

When exiting, the interactive login shell executes:

• ~/.bash_logout (if it exists)
• /etc/bash.bash_logout (if it exists)

For an interactive non-login shell (that's when you start gnome-terminal or tilix in X or Wayland), Bash just executes ~/.bashrc, if it exists. (So, no, /etc/bashrc is not invoked by Bash itself, but usually through ~/.bashrc, which by default sources /etc/bashrc.)

Because this is odd, the default ~/.bash_profile actually sources ~/.bashrc.

So for an interactive login shell, this happens (assuming the default config files from /etc/skel on Fedora 28):

1. /etc/profile is read,
2. whatever is in /etc/profile.d is included
3. /etc/bashrc is included, and the ${BASHRCSOURCED} variable is set to Y
4. ~/.bash_profile is read
5. ~/.bashrc is sourced through ~/.bash_profile
6. /etc/bashrc is sourced, again, this time through ~/.bashrc, but it's not actually parsed again, because ${BASHRCSOURCED} was already set to Y
7. neither ~/.bash_login, nor ~/.profile are sourced, because ~/.bash_profile exists
8. You get your shell

Finally, when Bash is invoked as the interpreter for a shell script, it will read ${BASH_ENV}, and it will read and execute the filename it finds in there. For Fedora 28, that's /usr/share/Modules/init/bash, owned by the environment-modules package.

Mind that this only happens if the shell script starts with the proper Bash shebang: #!/bin/bash or #!/usr/bin/bash, not with #!/bin/sh. Starting your shell script with #!/bin/sh will yield completely different results, as that will make Bash run in compatibility mode for old(er) shells.