10. Loading Prompt Colours Dynamically

10.1 A "Proof of Concept" Example

This is a "proof of concept" more than an attractive prompt: changing colours within the prompt dynamically. In this example, the colour of the host name changes depending on the load (as a warning).

#!/bin/bash
#   "hostloadcolour" - 17 October 98, by Giles
#
#   The idea here is to change the colour of the host name in the prompt, 
#   depending on a threshold load value.

# THRESHOLD_LOAD is the value of the one minute load (multiplied
# by one hundred) at which you want
# the prompt to change from COLOUR_LOW to COLOUR_HIGH
THRESHOLD_LOAD=200
COLOUR_LOW='1;34'
          # light blue
COLOUR_HIGH='1;31'
           # light red

function prompt_command {
ONE=$(uptime | sed -e "s/.*load average: \(.*\...\), \(.*\...\), \(.*\...\)/\1/" -e "s/ //g")
#   Apparently, "scale" in bc doesn't apply to multiplication, but does
#   apply to division.
ONEHUNDRED=$(echo -e "scale=0 \n $ONE/0.01 \nquit \n" | bc)
if [ $ONEHUNDRED -gt $THRESHOLD_LOAD ] 
then 
    HOST_COLOUR=$COLOUR_HIGH
        # Light Red
else
    HOST_COLOUR=$COLOUR_LOW
        # Light Blue
fi
}

function hostloadcolour {

PROMPT_COMMAND=prompt_command
PS1="[$(date +%H%M)][\u@\[\033[\$(echo -n \$HOST_COLOUR)m\]\h\[\033[0m\]:\w]$ "
}

Using your favorite editor, save this to a file named "hostloadcolour". If you have the Bashprompt package installed, this will work as a theme. If you don't, type source hostloadcolour and then hostloadcolour. Either way, "prompt_command" becomes a function in your environment. If you examine the code, you will notice that the colours ($COLOUR_HIGH and $COLOUR_LOW) are set using only a partial colour code, ie. "1;34" instead of "\[\033[1;34m\]", which I would have preferred. I have been unable to get it to work with the complete code. Please let me know if you manage this.