bash: update prompt to support displaying exit codes

.bashrc

@@ -61,11 +61,12 @@ if ${use_color} ; then
    # $@ - the color list (color=number)
    # $color_mod - a modifier to apply to the color (01 = bold, 00 = nothing)
    make_colors() {
+      local -- a
       for a; do
          local -- cname="col_${a%%=*}${modname:+_}${modname:-}"
          local -- val="${a#*=}"
          local -- ccode="${val}"
-         declare -g "$cname"='['"$ccode"m
+         declare -rg "$cname"='['"$ccode"m
          # declare -p "$cname"
       done
    }
@@ -73,12 +74,11 @@ if ${use_color} ; then
    # 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'
+      red=31 green=32 yellow=33 blue=34 purple=35 turquoise=36 white=37 black=38 grey=90 \
+      normal=00 bold=01 quiet=02 italic=03 under=04 bg=07 strike=09
+   col_end=''
    # shellcheck disable=SC2154
    if [[ ${EUID} == 0 ]] ; then
-      # shellcheck disable=
       ps1_color1="$col_bold$col_red"
       ps1_color2="$col_bold$col_blue"
       host='\h'
@@ -88,17 +88,19 @@ if ${use_color} ; then
       host='\u@\h'
    fi
 
-   PS1='$ps1_color1['$host'$ps1_color2 \W$ps1_color1]$status\$$col_end '
+   PS1='\[$ps1_color1\]['"$host"'\[$ps1_color2\] \W\[$ps1_color1\]]\[$status_col\]$status\[$ps1_color1\]\$\[$col_end\] '
 
    # assign $status to the exit code of the previous command, color it white on failure
    fmt_exit_status() {
-      # status=$?
-      case $? in
+      status=$?
+      status_col="$col_end"
+      case $status in
          (0)
-            status=" "
+            # shellcheck disable=SC2154
+            status_col+="$col_grey"
             ;;
          (*)
-            status="$col_normal$col_white$?$ps1_color1"
+            status_col+="$col_bold$col_white"
             ;;
       esac
    }