6.1. Colours

As mentioned before, non-printing escape sequences have to be enclosed in \[\033[ and \]. For colour escape sequences, they should also be followed by a lowercase m.

If you try out the following prompts in an xterm and find that you aren't seeing the colours named, check out your ~/.Xdefaults file (and possibly its bretheren) for lines like XTerm*Foreground: BlanchedAlmond. This can be commented out by placing an exclamation mark ("!") in front of it. Of course, this will also be dependent on what terminal emulator you're using. This is the likeliest place that your term foreground colours would be overridden.

To include blue text in the prompt:

PS1="\[\033[34m\][\$(date +%H%M)][\u@\h:\w]$ "

The problem with this prompt is that the blue colour that starts with the 34 colour code is never switched back to the regular colour, so any text you type after the prompt is still in the colour of the prompt. This is also a dark shade of blue, so combining it with the bold code might help:

PS1="\[\033[1;34m\][\$(date +%H%M)][\u@\h:\w]$\[\033[0m\] "

The prompt is now in light blue, and it ends by switching the colour back to nothing (whatever foreground colour you had previously).

Here are the rest of the colour equivalences:

Black       0;30     Dark Gray     1;30
Blue        0;34     Light Blue    1;34
Green       0;32     Light Green   1;32
Cyan        0;36     Light Cyan    1;36
Red         0;31     Light Red     1;31
Purple      0;35     Light Purple  1;35
Brown       0;33     Yellow        1;33
Light Gray  0;37     White         1;37

Daniel Dui (ddui@iee.org) points out that to be strictly accurate, we must mention that the list above is for colours at the console. In an xterm, the code 1;31 isn't "Light Red," but "Bold Red." This is true of all the colours.

You can also set background colours by using 44 for Blue background, 41 for a Red background, etc. There are no bold background colours. Combinations can be used, like Light Red text on a Blue background: \[\033[44;1;31m\], although setting the colours separately seems to work better (ie. \[\033[44m\]\[\033[1;31m\]). Other codes available include 4: Underscore, 5: Blink, 7: Inverse, and 8: Concealed.

Many people (myself included) object strongly to the "blink" attribute because it's extremely distracting and irritating. Fortunately, it doesn't work in any terminal emulators that I'm aware of - but it will still work on the console.

If you were wondering (as I did) "What use is a 'Concealed' attribute?!" - I saw it used in an example shell script (not a prompt) to allow someone to type in a password without it being echoed to the screen. However, this attribute doesn't seem to be honoured by many terms other than "Xterm."

Based on a prompt called "elite2" in the Bashprompt package (which I have modified to work better on a standard console, rather than with the special xterm fonts required to view the original properly), this is a prompt I've used a lot:

 
function elite
{

local GRAY="\[\033[1;30m\]"
local LIGHT_GRAY="\[\033[0;37m\]"
local CYAN="\[\033[0;36m\]"
local LIGHT_CYAN="\[\033[1;36m\]"
local NO_COLOUR="\[\033[0m\]"

case $TERM in
    xterm*|rxvt*)
        local TITLEBAR='\[\033]0;\u@\h:\w\007\]'
        ;;
    *)
        local TITLEBAR=""
        ;;
esac

local temp=$(tty)
local GRAD1=${temp:5}
PS1="$TITLEBAR\
$GRAY-$CYAN-$LIGHT_CYAN(\
$CYAN\u$GRAY@$CYAN\h\
$LIGHT_CYAN)$CYAN-$LIGHT_CYAN(\
$CYAN\#$GRAY/$CYAN$GRAD1\
$LIGHT_CYAN)$CYAN-$LIGHT_CYAN(\
$CYAN\$(date +%H%M)$GRAY/$CYAN\$(date +%d-%b-%y)\
$LIGHT_CYAN)$CYAN-$GRAY-\
$LIGHT_GRAY\n\
$GRAY-$CYAN-$LIGHT_CYAN(\
$CYAN\$$GRAY:$CYAN\w\
$LIGHT_CYAN)$CYAN-$GRAY-$LIGHT_GRAY " 
PS2="$LIGHT_CYAN-$CYAN-$GRAY-$NO_COLOUR "
}

I define the colours as temporary shell variables in the name of readability. It's easier to work with. The "GRAD1" variable is a check to determine what terminal you're on. Like the test to determine if you're working in an Xterm, it only needs to be done once. The prompt you see look like this, except in colour:

--(giles@gcsu202014)-(30/pts/6)-(0816/01-Aug-01)--
--($:~/tmp)--

To help myself remember what colours are available, I wrote a script that output all the colours to the screen. Daniel Crisman has supplied a much nicer version which I include below:

#!/bin/bash
#
#   This file echoes a bunch of color codes to the 
#   terminal to demonstrate what's available.  Each 
#   line is the color code of one forground color,
#   out of 17 (default + 16 escapes), followed by a 
#   test use of that color on all nine background 
#   colors (default + 8 escapes).
#

T='gYw'   # The test text

echo -e "\n                 40m     41m     42m     43m\
     44m     45m     46m     47m";

for FGs in '    m' '   1m' '  30m' '1;30m' '  31m' '1;31m' '  32m' \
           '1;32m' '  33m' '1;33m' '  34m' '1;34m' '  35m' '1;35m' \
           '  36m' '1;36m' '  37m' '1;37m';
  do FG=${FGs// /}
  echo -en " $FGs \033[$FG  $T  "
  for BG in 40m 41m 42m 43m 44m 45m 46m 47m;
    do echo -en "$EINS \033[$FG\033[$BG  $T  \033[0m";
  done
  echo;
done
echo