How to change the color scheme of the prompt based on user?

Question

My current prompt is colorized and edited as so -

#!/bin/bash

# GIT Prompt help
if tput setaf 1 &> /dev/null; then
    tput sgr0; # reset colors
    bold=$(tput bold);
    reset=$(tput sgr0);
    txtund=$(tput sgr 0 1);
    black=$(tput setaf 0);
    blue=$(tput setaf 33);
    cyan=$(tput setaf 37);
    green=$(tput setaf 64);
    orange=$(tput setaf 166);
    purple=$(tput setaf 125);
    red=$(tput setaf 124);
    violet=$(tput setaf 61);
    white=$(tput setaf 15);
    yellow=$(tput setaf 136);
else
    bold='';
    reset="\e[0m";
    black="\e[1;30m";
    blue="\e[1;34m";
    cyan="\e[1;36m";
    green="\e[1;32m";
    orange="\e[1;33m";
    purple="\e[1;35m";
    red="\e[1;31m";
    violet="\e[1;35m";
    white="\e[1;37m";
    yellow="\e[1;33m";
fi;
ORIG=$PS1
HOST=$HOSTNAME
PS1="\[${txtund}${green}\]${HOST}\[\[${reset}\]";
PS1+="\$(prompt_git \"\[${white}\] on \[${violet}\]\")";
PS1+="\[${reset}\]";
PS1+="\[ at - ${orange}\W\]";
PS1+="\[${reset}\]";
PS1+="\[ - \u \]";
PS1+="\n\$ ";

I know that the line PS1+="[ - \u ]"; will show me my current user. However, I want that section to be red if it is root. All other users should be the default color of gray. Is there a way to change the color in that section based off of current user or should I just declare a variable and use an IF statement to insert that section or a modified section with red as a color?

My expected output is gray named user for all normal users. Root should be red. This is BASH.

Answer 1

There are various ways you can check whether the user is root (to then set the PS1):

• the user's name, using $USER, $(whoami) (the output of $(whoami). N.B. the superuser can be called something else, but usually is called root.
• the user's ID, using $EUID or $UID (see here for some info). UID 0 is always the superuser.

So for instance you could replace the line PS1+="\[ - \u \]" with:

if [ $EUID -eq 0 ]; then
    PS1+="\[ - ${red}\u \]";
else
    PS1+="\[ - \u \]";
fi

You could also set another custom variable into the line:

PS1+="\[ - \u  ${usercolor}\]"

And use a conditional statement before if like this to change the colour:

if [ $EUID -eq 0 ]; then
    usercolor="\e[1;31m";
fi