Shell Configuration Files

By Danny Kalev, ITworld |  How-to

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
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:

clear
echo "don't forget to remove your homework exercises diskette from the
diskette drive!"

Other Shells
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.

A correction
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
typo.

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