bash: improvements to prompt

.bashrc

@@ -22,11 +22,11 @@ export SHELL_CONFIG_DIR="${SHELL_CONFIG_DIR:-"${XDG_CONFIG_HOME:-"$HOME/.config"
 
 # Change the window title of X terminals
 case ${TERM} in
-	xterm*|rxvt*|Eterm*|aterm|kterm|gnome*|interix|konsole*)
+   (screen*)
-		PROMPT_COMMAND='echo -ne "\033]0;${USER}@${HOSTNAME%%.*}:${PWD/#$HOME/\~}\007"'
+      PROMPT_COMMAND=('echo -ne "\033_${USER}@${HOSTNAME%%.*}:${PWD/#$HOME/\~}\033\\"')
       ;;
-	screen*)
+   (xterm*|rxvt*|Eterm*|aterm|kterm|gnome*|interix|konsole*|*)
-		PROMPT_COMMAND='echo -ne "\033_${USER}@${HOSTNAME%%.*}:${PWD/#$HOME/\~}\033\\"'
+      PROMPT_COMMAND=('echo -ne "\033]0;${USER}@${HOSTNAME%%.*}:${PWD/#$HOME/\~}\007"')
       ;;
 esac
 
@@ -49,6 +49,7 @@ match_lhs=""
 if ${use_color} ; then
    # Enable colors for ls, etc.  Prefer ~/.dir_colors #64489
    if type -P dircolors >/dev/null ; then
+      # shellcheck disable=SC2046
       if [[ -f ~/.dir_colors ]] ; then
          eval $(dircolors -b ~/.dir_colors)
       elif [[ -f /etc/DIR_COLORS ]] ; then
@@ -56,12 +57,54 @@ if ${use_color} ; then
       fi
    fi
 
+   # given a list of colors, make variables called `col_COLOR`
+   # $@ - the color list (color=number)
+   # $color_mod - a modifier to apply to the color (01 = bold, 00 = nothing)
+   make_colors() {
+      for a; do
+         local -- cname="col_${a%%=*}${modname:+_}${modname:-}"
+         local -- val="${a#*=}"
+         local -- ccode="${val}"
+         declare -g "$cname"='['"$ccode"m
+         # declare -p "$cname"
+      done
+   }
+
+   # set prompt  (see: man bash -> search for '^PROMPTING')
+
+   make_colors \
+      red=31 green=32 yellow=33 blue=34 purple=35 turquoise=36 white=38 white=37 \
+      normal=00 bold=01 quiet=02 italic=03 under=04 bg=07 gone=08 strike=09
+   col_end='(B'
+   # shellcheck disable=SC2154
    if [[ ${EUID} == 0 ]] ; then
-		PS1='\[\033[01;31m\][\h\[\033[01;36m\] \W\[\033[01;31m\]]\$\[\033[00m\] '
+      # shellcheck disable=
+      ps1_color1="$col_bold$col_red"
+      ps1_color2="$col_bold$col_blue"
+      host='\h'
    else
-		PS1='\[\033[01;32m\][\u@\h\[\033[01;37m\] \W\[\033[01;32m\]]\$\[\033[00m\] '
+      ps1_color1="$col_bold$col_green"
+      ps1_color2="$col_bold$col_white"
+      host='\u@\h'
    fi
 
+   PS1='$ps1_color1['$host'$ps1_color2 \W$ps1_color1]$status\$$col_end '
+
+   # assign $status to the exit code of the previous command, color it white on failure
+   fmt_exit_status() {
+      # status=$?
+      case $? in
+         (0)
+            status=" "
+            ;;
+         (*)
+            status="$col_normal$col_white$?$ps1_color1"
+            ;;
+      esac
+   }
+   PROMPT_COMMAND+=("fmt_exit_status")
+
+
 else
    if [[ ${EUID} == 0 ]] ; then
       # show root@ when we don't have colors