INVOCATION
A login shell is one whose first character of argument zero is a -, or one started with the --login option.
An interactive shell is one started without non-option arguments and without the -c option whose standard input and error
are both connected to terminals (as determined by isatty(3)), or one started with the -i option. PS1 is set and $-
includes i if bash is interactive, allowing a shell script or a startup file to test this state.
The following paragraphs describe how bash executes its startup files. If any of the files exist but cannot be read, bash
reports an error. Tildes are expanded in file names as described below under Tilde Expansion in the EXPANSION section.
When bash is invoked as an interactive login shell, or as a non-interactive shell with the --login option, it first reads
and executes commands from the file /etc/profile, if that file exists. After reading that file, it looks for ~/.bash_pro-
file, ~/.bash_login, and ~/.profile, in that order, and reads and executes commands from the first one that exists and is
readable. The --noprofile option may be used when the shell is started to inhibit this behavior.
When a login shell exits, bash reads and executes commands from the file ~/.bash_logout, if it exists.
When an interactive shell that is not a login shell is started, bash reads and executes commands from /etc/bash.bashrc and
~/.bashrc, if these files exist. This may be inhibited by using the --norc option. The --rcfile file option will force
bash to read and execute commands from file instead of /etc/bash.bashrc and ~/.bashrc.
