[Linuxcommand-announce] [LinuxCommand.org: Tips, News And Rants] Prompt Tricks

[William S. <bs...@pa...>]

Kind book reader Bruce Fowler sent me a note shortly after the book was
released providing some feedback on Chapter 14, "Customizing The
Prompt." He pointed out (quite rightly) that there are many practical
things you can do with the shell prompt that can make your command line
experience easier and more enjoyable. One of his favorites was simply
coloring the shell prompt so that it is easier to see in a long stream
of text output.

Your shell prompt is defined by the contents of a shell variable named
PS1. The variable contains a combination of literal text and special
codes that expand into various elements of the prompt when it is
displayed. We can easily modify our prompt to give it the color green.

First, we'll save a copy of our current prompt string in a new variable
named PS1_OLD:

me@linuxbox:~$ PS1_OLD="$PS1"
Later, if you want to revert to the original prompt settings, you can
do this:

me@linuxbox:~$ PS1="$PS1_OLD"
Next, we'll add ANSI escape sequences to the beginning and end of our
prompt string to set the color to green and back to its original color:

me@linuxbox:~$ PS1="\[\033[01;32m\]$PS1\[\033[00m\]"
Now, we have a green prompt!

me@linuxbox:~$

Let's break this prompt string down:

Element Meaning \[ Beginning of non-printing sequence. You need to tell
bash that the sequence that follows does not actually print characters
on the screen (it only sends control instructions to your terminal
emulator setting the color). bash would otherwise count the characters
and this would mess up bash's calculation of the cursor position which
it does to support command line editing. \033[01;32m ANSI sequence to
set foreground text green. \] End of non-printing sequence. $PS1
Original prompt string. We're embedding the original prompt string in
the middle to retain its design. \[ Beginning of non-printing sequence.
Again, the sequence that follows to reset the colors does not print
characters on the screen. \033[00m Sequence to reset attributes and
color to previous settings. \] End of non-printing sequence.
To make this change permenent, add this line to your .bashrc file:

PS1="\[\033[01;32m\]$PS1\[\033[00m\]"
Bruce also suggested making the prompt for the root account (if your
system is so equiped) a different color (like red) to remind you that
you are operating as the superuser.

Finally, Bruce included a short script that he picked up from a USENET
group which displays all the possible color and attributes supported by
ANSI:


#!/bin/sh ############################################################ #
Nico Golde (nico(at)ngolde.de) Homepage: http://www.ngolde.de # Last
change: Mon Feb 16 16:24:41 CET
2004 ############################################################ for
attr in 0 1 4 5 7 ; do
echo "----------------------------------------------------------------"
printf "ESC[%s;Foreground;Background - \n" $attr for fore in 30 31 32
33 34 35 36 37; do for back in 40 41 42 43 44 45 46 47; do
printf '\033[%s;%s;%sm %02s;%02s ' $attr $fore $back $fore $back done
printf '\n' done printf '\033[0m' done

When executed, the results look like this:

Further Reading

- Chapter 14 of The Linux Command Line

- Bash Prompt HOWTO

- The PROMPTING section of the bash man page

- ANSI Escape Codes


--
Posted By William Shotts to LinuxCommand.org: Tips, News And Rants at
2/10/2010 09:25:00 AM