Datasheet

Task 1.8: Manage the Shell Environment

Setup

To prepare for the task, log into your user account on your Linux system. (You can—and

should—perform this task as an ordinary user.) You may perform this task in either a text-

mode or a GUI login, but in the latter case, you must launch an xterm or similar command

prompt window.

Caveats

Performing this task as root poses the usual risks of accidentally damaging the installation. If

you badly corrupt your own bash configuration files, it’s conceivable (but unlikely) that you’ll

be unable to log in again. If this happens, use a root login to copy /etc/skel/.bashrc to your

user home directory and change the ownership of the copied file to your normal user account.

Procedure

To complete this task, you’ll change two environment variables. First you’ll do this tempo-

rarily so that your changes affect just a single login session. You’ll then make your changes

permanent by editing a user configuration file. At the end of this procedure, I describe several

other important environment variables, which you might choose to change if you so desire.

Adjusting Your Shell Prompt

The prompt in bash is controlled through the $PS1 variable. You set a variable by specifying the

variable name (minus the leading dollar sign, $), an equal sign (=), and the value to which you

want to set the variable. In most cases, you should surround the value of the prompt by quotes

("). For instance, you can set your bash prompt to read Your command? by typing the following:

$ PS1="Your command? "

Pay attention to the spaces (and lack thereof), particularly around the equal sign; adding

spaces around the equal sign will cause this command to fail. If you want a space between

the prompt and the point at which you begin typing, be sure to include one at the end of the

new prompt string.

The scenario presented earlier, though, specified that you want to include the time and date

in the command prompt. To do this, you must include special strings that serve as stand-ins

for other data. Specifically, the current date can be denoted by \d and the time can be denoted

by \@. Thus, you can set your prompt to include the date and time by issuing the following

command:

$ PS1="\d \@ $ "

The result might resemble the following, although of course the date and time shown in the

prompt will change with the real date and time:

Thu Jun 08 11:44 AM $

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