This week I will discuss shell configuration files and their uses.
Shell configuration files are executed automatically when you log in and
out of a shell. They initialize and configure a shell upon login and
perform cleanup operations upon logout.
BASH defines three configurations files: .bash_profile, .bashrc, and
.bash_logout. .bash_profile contains initialization commands that set
environment variables, a shell's prompt and so on. The .bashrc contains
commands that configure the shell, define command aliases and set
command shell options. .bash_profile is executed automatically when a
user logs into a shell, along with .bashrc. The .bash_logout file is
executed when the user logs out of a shell. .bash_logout contains
cleanup operations and other commands that you want the shell to execute
whenever a user logs out of a shell. For example, it can include
commands that clear the screen and print a farewell message. Unlike the
.bash_profile file, which is created automatically when you open a new
account, you have to create the .bash_logout by yourself using a text
editor such as vi, emacs, etc.
In the following example, the .bash_logout file contains commands that
clear the screen and print a reminder to the user to take her diskette
from the disk drive:
echo "don't forget to remove your homework exercises diskette from the
Other shells have similar configuration files, albeit with different
names. Thus, instead of the BASH .bash_profile, .bashrc, and
.bash_logout configuration files, TCSH uses the .login, .tcshrc and
.logout configuration files, respectively. Likewise, Z-shell uses the
files .zshenv, .zprofile, and .zlogin for initialization, .zshrc as a
configuration file equivalent to .bashrc, and .zlogout as the equivalent
of .bash_logout. The PDKSH shell uses the .profile and .kshrc files for
initialization and shell configuration, respectively.
In last week's newsletter, the meaning of the arguments +o and -o got
inverted. The +o argument actually turns a feature off whereas -o turns
it on. Thanks to all the readers who have drawn my attention to this