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Featured Article: Getting a colored shell prompt

by Richard Keech

Working in the world of the Linux command line is normally a monochromatic experience. However, the output of some commands, like ls, can utilise color-coded output to convey information in a more powerful way. Carefully chosen colors in interfaces can enhance their useability. Let's apply this thinking to the command prompt.

The main terminal emulator programs in Red Hat (gnome-terminal, konsole, xterm) can interpret standard escape sequences for cursor control and character effects. This includes the setting of colors. These escape sequences are standardised in ISO/IEC 6429:1992 "Information technology -- Control functions for coded character sets". On Red Hat Linux a reference to these can be found in the dir_colors(5) man page. So setting a colored prompt involves embedding ISO 6429 escape sequences in the Bash prompt string variable ($PS).

Aside from visual interest, why bother? Well, first it aids readability since the coloured prompts delimit the command-display-command-display in a terminal window. Second, it can aid security by making root shells more obvious. I use red to indicate a root shell. This makes it less likely that you will inadvertantly enter an inappropriate command in a root shell.

To illustrate the usefullness, shown here are two terminal windows, identical except for the colored prompts. Side-by-side comparison shows how the colored prompts aid readability, and emphasise the part where the shell has root privilege.

To achieve this, get the file colorprompt.sh from http://people.redhat.com/rkeech/#color and put it in /etc/profile.d/ where it should be executable.

The colorprompt.sh file (simplified) looks like this:

lc='\[\e[1;' # lead-in character
RED=${lc}31m;
PURPLE=${lc}35m
RC=${lc}0m # reset character

if [ "$USER" = "root" ]
then
pc=$RED
else
pc=$PURPLE
fi

PS1="${pc}\]\u@\h \W\\$ ${RC}\]"

Notes; this method is written with Bash in mind. It is expected to work for other shells in an equivalent manner. Its use with the screen command has not been tested.

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