PATH HOWTO: Shells

In login, the name of the shell is preceded with '-', for example bash is called as '-bash'. This signals to the shell that it is a 'login' shell. In this case, the shell executes the 'login' initialization files. Otherwise some lighter initialization is performed. Additionally, the shell checks if it is interactive - are the commands coming from file or interactive tty. This modifies the shell initialization so that a non-interactive non-login shell is initialized very lightly - bash do not execute any initialization file in this case!

6.1 bash

As a normal login shell, bash 'sources' system-wide file /etc/profile, where the system environment and path can be set for bash users. However, it is not run when the system interprets the shell as non-interactive. The most important case is in rsh, where remote command is executed in the neighboring machine. The /etc/profile is not run and the path is inherited from rsh daemon.

bash receives command line arguments -login and -i that can be used to set the shell as a login shell or interactive shell respectively.

The user can overwrite values set in /etc/profile by creating a file ~/.bash_profile, ~/.bash_login or ~/.profile. Note that just the first one of these is executed thus differing of the logic of csh initialization. ~/.bash_login is not executed specially for login shells and if .bash_profile exists, it is not executed at all!

If bash is used with name sh instead of the name bash, it emulates original Bourne shell initialization: it sources just files /etc/profile and ~/.profile and just for login shells.