theme/norbu: `shellcheck` && `shfmt`

# Conflicts:
#	clean_files.txt

clean_files.txt

@@ -153,6 +153,7 @@ themes/command_duration.theme.bash
 themes/easy
 themes/essential
 themes/modern
+themes/norbu
 themes/pete
 themes/powerline
 themes/pure

themes/norbu/norbu.theme.bash

@@ -1,21 +1,23 @@
-#!/usr/bin/env bash
+# shellcheck shell=bash
+# shellcheck disable=SC2034 # Expected behavior for themes.
 
 function set_prompt_symbol() {
-    if test $1 -eq 0 ; then
-	PROMPT_SYMBOL=">_"
+	if [[ $1 -eq 0 ]]; then
+		prompt_symbol=">_"
 	else
-	PROMPT_SYMBOL="${orange}>_${normal}"
+		prompt_symbol="${orange?}>_${normal?}"
 	fi
 }
+
 function prompt_command() {
-    set_prompt_symbol $?
-    if test -z "$VIRTUAL_ENV" ; then
-	PYTHON_VIRTUALENV=""
-    else
-	PYTHON_VIRTUALENV="${bold_yellow}[`basename \"$VIRTUAL_ENV\"`]"
+	local ret_val="$?" prompt_symbol scm_prompt_info
+	if [[ -n "${VIRTUAL_ENV:-}" ]]; then
+		PYTHON_VIRTUALENV="${bold_yellow?}[${VIRTUAL_ENV##*/}]"
 	fi
 
-    PS1="${bold_orange}${PYTHON_VIRTUALENV}${reset_color}${bold_green}[\w]${bold_blue}\[$(scm_prompt_info)\]${normal} \n${PROMPT_SYMBOL} "
+	scm_prompt_info="$(scm_prompt_info)"
+	set_prompt_symbol "${ret_val}"
+	PS1="${bold_orange?}${PYTHON_VIRTUALENV:-}${reset_color?}${bold_green?}[\w]${bold_blue?}[${scm_prompt_info}]${normal?} \n${prompt_symbol} "
 }
 
 # scm themeing