diff --git a/clean_files.txt b/clean_files.txt
index bfc5596144..1c19acbc7c 100644
--- a/clean_files.txt
+++ b/clean_files.txt
@@ -41,6 +41,7 @@ themes/atomic
 themes/axin
 themes/bakke
 themes/barbuk
+themes/base.theme.bash
 themes/binaryanomaly
 themes/bira
 themes/bobby
@@ -74,14 +75,25 @@ themes/kitsune
 themes/lambda
 themes/liquidprompt
 themes/luan
+themes/mairan
+themes/mbriggs
+themes/metal
+themes/minimal
 themes/modern
+themes/modern-t
+themes/modern-time
+themes/morris
+themes/n0qorg
+themes/newin
 themes/norbu
+themes/nwinkler
 themes/oh-my-posh
 themes/p4helpers.theme.bash
 themes/pete
 themes/powerline
 themes/powerline-multiline
 themes/powerline-naked
+themes/powerline-plain
 themes/pure
 themes/purity
 themes/rjorgenson
diff --git a/themes/mairan/mairan.theme.bash b/themes/mairan/mairan.theme.bash
index 65ef7ac1d3..2e6cec9930 100644
--- a/themes/mairan/mairan.theme.bash
+++ b/themes/mairan/mairan.theme.bash
@@ -1,3 +1,5 @@
+# shellcheck shell=bash
+# shellcheck disable=SC2034
 # Mairan Bash Prompt, inspired by "Zork"
 
 if tput setaf 1 &> /dev/null; then
@@ -34,11 +36,11 @@ BRACKET_COLOR=$ORANGE
 SCM_THEME_PROMPT_PREFIX=""
 SCM_THEME_PROMPT_SUFFIX=""
 
-SCM_THEME_PROMPT_DIRTY=" ${bold_red}✗${normal}"
-SCM_THEME_PROMPT_CLEAN=" ${bold_green}✓${normal}"
-SCM_GIT_CHAR="${bold_green}±${normal}"
-SCM_SVN_CHAR="${bold_cyan}⑆${normal}"
-SCM_HG_CHAR="${bold_red}☿${normal}"
+SCM_THEME_PROMPT_DIRTY=" ${bold_red?}✗${normal?}"
+SCM_THEME_PROMPT_CLEAN=" ${bold_green?}✓${normal?}"
+SCM_GIT_CHAR="${bold_green?}±${normal?}"
+SCM_SVN_CHAR="${bold_cyan?}⑆${normal?}"
+SCM_HG_CHAR="${bold_red?}☿${normal?}"
 
 #Mysql Prompt
 export MYSQL_PS1="(\u@\h) [\d]> "
@@ -55,23 +57,25 @@ esac
 PS3=">> "
 
 __my_rvm_ruby_version() {
-	local gemset=$(echo $GEM_HOME | awk -F'@' '{print $2}')
+	local gemset
+	gemset=$(echo "$GEM_HOME" | awk -F'@' '{print $2}')
 	[ "$gemset" != "" ] && gemset="@$gemset"
-	local version=$(echo $MY_RUBY_HOME | awk -F'-' '{print $2}')
+	local version
+	version=$(echo "$MY_RUBY_HOME" | awk -F'-' '{print $2}')
 	local full="$version$gemset"
 	[ "$full" != "" ] && echo "[$full]"
 }
 
 is_vim_shell() {
-	if [ ! -z "$VIMRUNTIME" ]; then
-		echo "[${cyan}vim shell${normal}]"
+	if [ -n "$VIMRUNTIME" ]; then
+		echo "[${cyan?}vim shell${normal?}]"
 	fi
 }
 
 # show chroot if exist
 chroot() {
 	if [ -n "$debian_chroot" ]; then
-		my_ps_chroot="${bold_cyan}$debian_chroot${normal}"
+		my_ps_chroot="${bold_cyan?}$debian_chroot${normal?}"
 		echo "($my_ps_chroot)"
 	fi
 }
@@ -79,7 +83,7 @@ chroot() {
 # show virtualenvwrapper
 my_ve() {
 	if [ -n "$VIRTUAL_ENV" ]; then
-		my_ps_ve="${bold_purple}$ve${normal}"
+		my_ps_ve="${bold_purple?}$ve${normal?}"
 		echo "($my_ps_ve)"
 	fi
 	echo ""
@@ -87,12 +91,12 @@ my_ve() {
 
 prompt() {
 	SCM_PROMPT_FORMAT="[%s$GREEN%s]"
-	my_ps_host="$BOLD$ORANGE\h${normal}"
+	my_ps_host="$BOLD$ORANGE\h${normal?}"
 	# yes, these are the the same for now ...
-	my_ps_host_root="$ORANGE\h${normal}"
+	my_ps_host_root="$ORANGE\h${normal?}"
 
-	my_ps_user="$BOLD$GREEN\u${normal}"
-	my_ps_root="${bold_red}\u${normal}"
+	my_ps_user="$BOLD$GREEN\u${normal?}"
+	my_ps_root="${bold_red?}\u${normal?}"
 
 	if [ -n "$VIRTUAL_ENV" ]; then
 		ve=$(basename "$VIRTUAL_ENV")
@@ -101,12 +105,12 @@ prompt() {
 	# nice prompt
 	case "$(id -u)" in
 		0)
-			PS1="\n${TITLEBAR}${BRACKET_COLOR}┌─${normal}$(my_ve)$(chroot)[$my_ps_root][$my_ps_host_root]$(scm_prompt)$(__my_rvm_ruby_version)[${green}\w${normal}]$(is_vim_shell)${BRACKET_COLOR}
-└─▪ ${prompt_symbol} ${normal}"
+			PS1="\n${TITLEBAR}${BRACKET_COLOR}┌─${normal?}$(my_ve)$(chroot)[$my_ps_root][$my_ps_host_root]$(scm_prompt)$(__my_rvm_ruby_version)[${green?}\w${normal?}]$(is_vim_shell)${BRACKET_COLOR}
+└─▪ ${prompt_symbol} ${normal?}"
 			;;
 		*)
-			PS1="\n${TITLEBAR}${BRACKET_COLOR}┌─${normal}$(my_ve)$(chroot)[$my_ps_user][$my_ps_host]$(scm_prompt)${normal}$(__my_rvm_ruby_version)[${green}\w${normal}]$(is_vim_shell)${BRACKET_COLOR}
-└─▪ ${prompt_symbol} ${normal}"
+			PS1="\n${TITLEBAR}${BRACKET_COLOR}┌─${normal?}$(my_ve)$(chroot)[$my_ps_user][$my_ps_host]$(scm_prompt)${normal?}$(__my_rvm_ruby_version)[${green?}\w${normal?}]$(is_vim_shell)${BRACKET_COLOR}
+└─▪ ${prompt_symbol} ${normal?}"
 			;;
 	esac
 }
diff --git a/themes/mbriggs/mbriggs.theme.bash b/themes/mbriggs/mbriggs.theme.bash
index 9e1511e316..7ed8851b10 100644
--- a/themes/mbriggs/mbriggs.theme.bash
+++ b/themes/mbriggs/mbriggs.theme.bash
@@ -1,16 +1,18 @@
+# shellcheck shell=bash
+# shellcheck disable=SC2034
 # ------------------------------------------------------------------#
 #          FILE: mbriggs.zsh-theme                                  #
 #            BY: Matt Briggs (matt@mattbriggs.net)                  #
 #      BASED ON: smt by Stephen Tudor (stephen@tudorstudio.com)     #
 # ------------------------------------------------------------------#
 
-SCM_THEME_PROMPT_DIRTY="${red}⚡${reset_color}"
-SCM_THEME_PROMPT_AHEAD="${red}!${reset_color}"
-SCM_THEME_PROMPT_CLEAN="${green}✓${reset_color}"
+SCM_THEME_PROMPT_DIRTY="${red?}⚡${reset_color?}"
+SCM_THEME_PROMPT_AHEAD="${red?}!${reset_color?}"
+SCM_THEME_PROMPT_CLEAN="${green?}✓${reset_color?}"
 SCM_THEME_PROMPT_PREFIX=" "
 SCM_THEME_PROMPT_SUFFIX=""
-GIT_SHA_PREFIX=" ${yellow}"
-GIT_SHA_SUFFIX="${reset_color}"
+GIT_SHA_PREFIX=" ${yellow?}"
+GIT_SHA_SUFFIX="${reset_color?}"
 
 function git_short_sha() {
 	SHA=$(git rev-parse --short HEAD 2> /dev/null) && echo "$GIT_SHA_PREFIX$SHA$GIT_SHA_SUFFIX"
@@ -18,11 +20,14 @@ function git_short_sha() {
 
 function prompt() {
 	local return_status=""
-	local ruby="${red}$(ruby_version_prompt)${reset_color}"
-	local user_host="${green}\h${reset_color}"
+	local ruby
+	ruby="${red?}$(ruby_version_prompt)${reset_color?}"
+	local user_host
+	user_host="${green?}\h${reset_color?}"
 	local current_path="\w"
 	local n_commands="\!"
-	local git_branch="$(git_short_sha)$(scm_prompt_info)"
+	local git_branch
+	git_branch="$(git_short_sha)$(scm_prompt_info)"
 	local prompt_symbol='λ'
 	local open='('
 	local close=')'
diff --git a/themes/metal/metal.theme.bash b/themes/metal/metal.theme.bash
index e68a90a9b7..75a4e8bae2 100644
--- a/themes/metal/metal.theme.bash
+++ b/themes/metal/metal.theme.bash
@@ -1,4 +1,5 @@
-#!/usr/bin/env bash
+# shellcheck shell=bash
+# shellcheck disable=SC2034
 
 # Emoji-based theme to display source control management and
 # virtual environment info beside the ordinary bash prompt.
@@ -21,11 +22,11 @@ VIRTUALENV_THEME_PROMPT_SUFFIX=""
 # SCM prompts
 SCM_NONE_CHAR=""
 SCM_GIT_CHAR="[±] "
-SCM_GIT_BEHIND_CHAR="${red}↓${normal}"
-SCM_GIT_AHEAD_CHAR="${bold_green}↑${normal}"
+SCM_GIT_BEHIND_CHAR="${red?}↓${normal?}"
+SCM_GIT_AHEAD_CHAR="${bold_green?}↑${normal?}"
 SCM_GIT_UNTRACKED_CHAR="⌀"
-SCM_GIT_UNSTAGED_CHAR="${bold_yellow}•${normal}"
-SCM_GIT_STAGED_CHAR="${bold_green}+${normal}"
+SCM_GIT_UNSTAGED_CHAR="${bold_yellow?}•${normal?}"
+SCM_GIT_STAGED_CHAR="${bold_green?}+${normal?}"
 
 SCM_THEME_PROMPT_DIRTY=""
 SCM_THEME_PROMPT_CLEAN=""
@@ -33,8 +34,8 @@ SCM_THEME_PROMPT_PREFIX=""
 SCM_THEME_PROMPT_SUFFIX=""
 
 # Git status prompts
-GIT_THEME_PROMPT_DIRTY=" ${red}✗${normal}"
-GIT_THEME_PROMPT_CLEAN=" ${bold_green}✓${normal}"
+GIT_THEME_PROMPT_DIRTY=" ${red?}✗${normal?}"
+GIT_THEME_PROMPT_CLEAN=" ${bold_green?}✓${normal?}"
 GIT_THEME_PROMPT_PREFIX=""
 GIT_THEME_PROMPT_SUFFIX=""
 
@@ -61,19 +62,19 @@ function virtualenv_prompt {
 
 # Rename tab
 function tabname {
-	printf "\e]1;$1\a"
+	printf '\e]1;%s\a' "$1"
 }
 
 # Rename window
 function winname {
-	printf "\e]2;$1\a"
+	printf '\e]2;%s\a' "$1"
 }
 
 # PROMPT OUTPUT ===============================================================
 
 # Displays the current prompt
 function prompt_command() {
-	PS1="\n${icon_start}$(virtualenv_prompt)${icon_user}${bold_green}\u${normal}${icon_host}${bold_cyan}\h${normal}${icon_directory}${bold_purple}\W${normal}\$([[ -n \$(git branch 2> /dev/null) ]] && echo \" on ${icon_branch}  \")${white}$(scm_prompt_info)${normal}\n${icon_end}"
+	PS1="\n${icon_start}$(virtualenv_prompt)${icon_user}${bold_green?}\u${normal?}${icon_host}${bold_cyan?}\h${normal?}${icon_directory}${bold_purple?}\W${normal?}\$([[ -n \$(git branch 2> /dev/null) ]] && echo \" on ${icon_branch}  \")${white?}$(scm_prompt_info)${normal?}\n${icon_end}"
 	PS2="${icon_end}"
 }
 
diff --git a/themes/minimal/minimal.theme.bash b/themes/minimal/minimal.theme.bash
index 2bf807c16f..0256ccaf6a 100644
--- a/themes/minimal/minimal.theme.bash
+++ b/themes/minimal/minimal.theme.bash
@@ -1,12 +1,13 @@
-#!/usr/bin/env bash
+# shellcheck shell=bash
+# shellcheck disable=SC2034
 
-SCM_THEME_PROMPT_PREFIX="${cyan}(${green}"
-SCM_THEME_PROMPT_SUFFIX="${cyan})"
-SCM_THEME_PROMPT_DIRTY=" ${red}✗"
-SCM_THEME_PROMPT_CLEAN=" ${green}✓"
+SCM_THEME_PROMPT_PREFIX="${cyan?}(${green?}"
+SCM_THEME_PROMPT_SUFFIX="${cyan?})"
+SCM_THEME_PROMPT_DIRTY=" ${red?}✗"
+SCM_THEME_PROMPT_CLEAN=" ${green?}✓"
 
 prompt() {
-	PS1="$(scm_prompt_info)${reset_color} ${cyan}\W${reset_color} "
+	PS1="$(scm_prompt_info)${reset_color?} ${cyan?}\W${reset_color?} "
 }
 
 safe_append_prompt_command prompt
diff --git a/themes/modern-t/modern-t.theme.bash b/themes/modern-t/modern-t.theme.bash
index c0a5b556e7..9051ebcc49 100644
--- a/themes/modern-t/modern-t.theme.bash
+++ b/themes/modern-t/modern-t.theme.bash
@@ -1,3 +1,5 @@
+# shellcheck shell=bash
+# shellcheck disable=SC2034
 # The "modern-t" theme is a "modern" theme variant with support
 # for "t", the minimalist python todo list utility by Steve Losh.
 # Get and install "t" at https://github.com/sjl/t#installing-t
@@ -8,11 +10,11 @@
 SCM_THEME_PROMPT_PREFIX=""
 SCM_THEME_PROMPT_SUFFIX=""
 
-SCM_THEME_PROMPT_DIRTY=" ${bold_red}✗${normal}"
-SCM_THEME_PROMPT_CLEAN=" ${bold_green}✓${normal}"
-SCM_GIT_CHAR="${bold_green}±${normal}"
-SCM_SVN_CHAR="${bold_cyan}⑆${normal}"
-SCM_HG_CHAR="${bold_red}☿${normal}"
+SCM_THEME_PROMPT_DIRTY=" ${bold_red?}✗${normal?}"
+SCM_THEME_PROMPT_CLEAN=" ${bold_green?}✓${normal?}"
+SCM_GIT_CHAR="${bold_green?}±${normal?}"
+SCM_SVN_CHAR="${bold_cyan?}⑆${normal?}"
+SCM_HG_CHAR="${bold_red?}☿${normal?}"
 
 case $TERM in
 	xterm*)
@@ -26,21 +28,22 @@ esac
 PS3=">> "
 
 is_vim_shell() {
-	if [ ! -z "$VIMRUNTIME" ]; then
-		echo "[${cyan}vim shell${normal}]"
+	if [ -n "$VIMRUNTIME" ]; then
+		echo "[${cyan?}vim shell${normal?}]"
 	fi
 }
 
 prompt() {
+	local last_status=$?
 	SCM_PROMPT_FORMAT='[%s][%s]'
-	if [ $? -ne 0 ]; then
+	if [ "$last_status" -ne 0 ]; then
 		# Yes, the indenting on these is weird, but it has to be like
 		# this otherwise it won't display properly.
 
-		PS1="${TITLEBAR}${bold_red}┌─[${cyan}$(t | wc -l | sed -e's/ *//')${reset_color}]${reset_color}$(scm_prompt)[${cyan}\W${normal}]$(is_vim_shell)
-${bold_red}└─▪${normal} "
+		PS1="${TITLEBAR}${bold_red?}┌─[${cyan?}$(t | wc -l | sed -e's/ *//')${reset_color?}]${reset_color?}$(scm_prompt)[${cyan?}\W${normal?}]$(is_vim_shell)
+${bold_red?}└─▪${normal?} "
 	else
-		PS1="${TITLEBAR}┌─[${cyan}$(t | wc -l | sed -e's/ *//')${reset_color}]$(scm_prompt)[${cyan}\W${normal}]$(is_vim_shell)
+		PS1="${TITLEBAR}┌─[${cyan?}$(t | wc -l | sed -e's/ *//')${reset_color?}]$(scm_prompt)[${cyan?}\W${normal?}]$(is_vim_shell)
 └─▪ "
 	fi
 }
diff --git a/themes/modern-time/modern-time.theme.bash b/themes/modern-time/modern-time.theme.bash
index ceb2f5ede3..0fafaba194 100644
--- a/themes/modern-time/modern-time.theme.bash
+++ b/themes/modern-time/modern-time.theme.bash
@@ -1,14 +1,16 @@
+# shellcheck shell=bash
+# shellcheck disable=SC2034
 # Modified version of the original modern theme in bash-it
 # Removes the battery charge and adds the current time
 
 SCM_THEME_PROMPT_PREFIX=""
 SCM_THEME_PROMPT_SUFFIX=""
 
-SCM_THEME_PROMPT_DIRTY=" ${bold_red}✗${normal}"
-SCM_THEME_PROMPT_CLEAN=" ${bold_green}✓${normal}"
-SCM_GIT_CHAR="${bold_green}±${normal}"
-SCM_SVN_CHAR="${bold_cyan}⑆${normal}"
-SCM_HG_CHAR="${bold_red}☿${normal}"
+SCM_THEME_PROMPT_DIRTY=" ${bold_red?}✗${normal?}"
+SCM_THEME_PROMPT_CLEAN=" ${bold_green?}✓${normal?}"
+SCM_GIT_CHAR="${bold_green?}±${normal?}"
+SCM_SVN_CHAR="${bold_cyan?}⑆${normal?}"
+SCM_HG_CHAR="${bold_red?}☿${normal?}"
 
 case $TERM in
 	xterm*)
@@ -22,8 +24,8 @@ esac
 PS3=">> "
 
 is_vim_shell() {
-	if [ ! -z "$VIMRUNTIME" ]; then
-		echo "[${cyan}vim shell${normal}]"
+	if [ -n "$VIMRUNTIME" ]; then
+		echo "[${cyan?}vim shell${normal?}]"
 	fi
 }
 
@@ -33,14 +35,15 @@ modern_current_time_prompt() {
 
 prompt() {
 	SCM_PROMPT_FORMAT='[%s][%s]'
-	if [ $? -ne 0 ]; then
+	local last_status=$?
+	if [ $last_status -ne 0 ]; then
 		# Yes, the indenting on these is weird, but it has to be like
 		# this otherwise it won't display properly.
 
-		PS1="${TITLEBAR}${bold_red}┌─${reset_color}$(scm_prompt)$(modern_current_time_prompt)[${cyan}\W${normal}]$(is_vim_shell)
-${bold_red}└─▪${normal} "
+		PS1="${TITLEBAR}${bold_red?}┌─${reset_color?}$(scm_prompt)$(modern_current_time_prompt)[${cyan?}\W${normal?}]$(is_vim_shell)
+${bold_red?}└─▪${normal?} "
 	else
-		PS1="${TITLEBAR}┌─$(scm_prompt)$(modern_current_time_prompt)[${cyan}\W${normal}]$(is_vim_shell)
+		PS1="${TITLEBAR}┌─$(scm_prompt)$(modern_current_time_prompt)[${cyan?}\W${normal?}]$(is_vim_shell)
 └─▪ "
 	fi
 }
diff --git a/themes/morris/morris.theme.bash b/themes/morris/morris.theme.bash
index 58b1bad816..55cce12f90 100644
--- a/themes/morris/morris.theme.bash
+++ b/themes/morris/morris.theme.bash
@@ -1,3 +1,5 @@
+# shellcheck shell=bash
+# shellcheck disable=SC2034
 # prompt theming
 
 # added TITLEBAR for updating the tab and window titles with the pwd
@@ -18,9 +20,9 @@ function prompt_command() {
 }
 
 # scm theming
-SCM_THEME_PROMPT_DIRTY=" ${red}✗"
-SCM_THEME_PROMPT_CLEAN=" ${bold_green}✓"
-SCM_THEME_PROMPT_PREFIX="${green}("
-SCM_THEME_PROMPT_SUFFIX="${green})${reset_color}"
+SCM_THEME_PROMPT_DIRTY=" ${red?}✗"
+SCM_THEME_PROMPT_CLEAN=" ${bold_green?}✓"
+SCM_THEME_PROMPT_PREFIX="${green?}("
+SCM_THEME_PROMPT_SUFFIX="${green?})${reset_color?}"
 
 safe_append_prompt_command prompt_command
diff --git a/themes/n0qorg/n0qorg.theme.bash b/themes/n0qorg/n0qorg.theme.bash
index b82a17f3d4..e81767386b 100644
--- a/themes/n0qorg/n0qorg.theme.bash
+++ b/themes/n0qorg/n0qorg.theme.bash
@@ -1,4 +1,5 @@
-#!/usr/bin/env bash
+# shellcheck shell=bash
+# shellcheck disable=SC2034
 # n0qorg theme by Florian Baumann <flo@noqqe.de>
 
 ## look-a-like
@@ -6,17 +7,17 @@
 # for example:
 # ananas ~/Code/bash-it/themes (master*)»
 function prompt_command() {
-	PS1="${bold_blue}[$(hostname)]${normal} \w${normal} ${bold_white}[$(git_prompt_info)]${normal}» "
+	PS1="${bold_blue?}[$(hostname)]${normal?} \w${normal?} ${bold_white?}[$(git_prompt_info)]${normal?}» "
 }
 
 safe_append_prompt_command prompt_command
 
 ## git-theme
 # feel free to change git chars.
-GIT_THEME_PROMPT_DIRTY="${bold_blue}*${bold_white}"
+GIT_THEME_PROMPT_DIRTY="${bold_blue?}*${bold_white?}"
 GIT_THEME_PROMPT_CLEAN=""
-GIT_THEME_PROMPT_PREFIX="${bold_blue}(${bold_white}"
-GIT_THEME_PROMPT_SUFFIX="${bold_blue})"
+GIT_THEME_PROMPT_PREFIX="${bold_blue?}(${bold_white?}"
+GIT_THEME_PROMPT_SUFFIX="${bold_blue?})"
 
 ## alternate chars
 #
diff --git a/themes/newin/newin.theme.bash b/themes/newin/newin.theme.bash
index cabd024fe1..8f9a052389 100644
--- a/themes/newin/newin.theme.bash
+++ b/themes/newin/newin.theme.bash
@@ -1,13 +1,14 @@
-#!/usr/bin/env bash
+# shellcheck shell=bash
+# shellcheck disable=SC2034
 
-SCM_THEME_PROMPT_DIRTY=" ${red}✗"
-SCM_THEME_PROMPT_CLEAN=" ${green}✓"
-SCM_THEME_PROMPT_PREFIX=" ${purple}|${green} "
-SCM_THEME_PROMPT_SUFFIX="${purple} |"
+SCM_THEME_PROMPT_DIRTY=" ${red?}✗"
+SCM_THEME_PROMPT_CLEAN=" ${green?}✓"
+SCM_THEME_PROMPT_PREFIX=" ${purple?}|${green?} "
+SCM_THEME_PROMPT_SUFFIX="${purple?} |"
 
 prompt() {
 	exit_code=$?
-	PS1="$(if [[ ${exit_code} = 0 ]]; then echo "${green}${exit_code}"; else echo "${red}${exit_code}"; fi) ${yellow}\t ${cyan}\w$(scm_prompt_info)${reset_color}\n${orange}$ ${reset_color}"
+	PS1="$(if [[ ${exit_code} = 0 ]]; then echo "${green?}${exit_code}"; else echo "${red?}${exit_code}"; fi) ${yellow?}\t ${cyan?}\w$(scm_prompt_info)${reset_color?}\n${orange?}$ ${reset_color?}"
 }
 
 safe_append_prompt_command prompt
diff --git a/themes/nwinkler/nwinkler.theme.bash b/themes/nwinkler/nwinkler.theme.bash
index 5bb66aee69..b72c33e180 100644
--- a/themes/nwinkler/nwinkler.theme.bash
+++ b/themes/nwinkler/nwinkler.theme.bash
@@ -1,4 +1,5 @@
 # shellcheck shell=bash
+# shellcheck disable=SC2034
 
 # Two line prompt showing the following information:
 # (time) SCM [username@hostname] pwd (SCM branch SCM status)
@@ -15,8 +16,8 @@
 # The exit code functionality currently doesn't work if you are using the 'fasd' plugin,
 # since 'fasd' is messing with the $PROMPT_COMMAND
 
-PROMPT_END_CLEAN="${green}→${reset_color}"
-PROMPT_END_DIRTY="${red}→${reset_color}"
+PROMPT_END_CLEAN="${green?}→${reset_color?}"
+PROMPT_END_DIRTY="${red?}→${reset_color?}"
 
 function prompt_end() {
 	echo -e "$PROMPT_END"
@@ -31,15 +32,15 @@ prompt_setter() {
 	fi
 	# Save history
 	_save-and-reload-history 1
-	PS1="($(clock_prompt)) $(scm_char) [${blue}\u${reset_color}@${green}\H${reset_color}] ${yellow}\w${reset_color}$(scm_prompt_info) ${reset_color}\n$(prompt_end) "
+	PS1="($(clock_prompt)) $(scm_char) [${blue?}\u${reset_color?}@${green?}\H${reset_color?}] ${yellow?}\w${reset_color?}$(scm_prompt_info) ${reset_color?}\n$(prompt_end) "
 	PS2='> '
 	PS4='+ '
 }
 
 safe_append_prompt_command prompt_setter
 
-SCM_THEME_PROMPT_DIRTY=" ${bold_red}✗${normal}"
-SCM_THEME_PROMPT_CLEAN=" ${bold_green}✓${normal}"
+SCM_THEME_PROMPT_DIRTY=" ${bold_red?}✗${normal?}"
+SCM_THEME_PROMPT_CLEAN=" ${bold_green?}✓${normal?}"
 SCM_THEME_PROMPT_PREFIX=" ("
 SCM_THEME_PROMPT_SUFFIX=")"
 RVM_THEME_PROMPT_PREFIX=" ("
diff --git a/themes/powerline-plain/powerline-plain.base.bash b/themes/powerline-plain/powerline-plain.base.bash
index c077a089fc..46edcf61c9 100644
--- a/themes/powerline-plain/powerline-plain.base.bash
+++ b/themes/powerline-plain/powerline-plain.base.bash
@@ -1,9 +1,11 @@
+# shellcheck shell=bash
 . "$BASH_IT/themes/powerline/powerline.base.bash"
 
 function __powerline_left_segment {
 	local OLD_IFS="${IFS}"
 	IFS="|"
-	local params=($1)
+	local -a params
+	IFS='|' read -ra params <<< "$1"
 	IFS="${OLD_IFS}"
 	local pad_before_segment=" "
 
@@ -18,11 +20,11 @@ function __powerline_left_segment {
 		# Since the previous segment wasn't the last segment, add padding, if needed
 		#
 		if [[ "${POWERLINE_COMPACT_BEFORE_SEPARATOR}" -eq 0 ]]; then
-			LEFT_PROMPT+="$(set_color - ${LAST_SEGMENT_COLOR}) ${normal}"
+			LEFT_PROMPT+="$(set_color - "${LAST_SEGMENT_COLOR}") ${normal:-}"
 		fi
 	fi
 
-	LEFT_PROMPT+="$(set_color - ${params[1]})${pad_before_segment}${params[0]}${normal}"
+	LEFT_PROMPT+="$(set_color - "${params[1]}")${pad_before_segment}${params[0]}${normal:-}"
 	LAST_SEGMENT_COLOR=${params[1]}
 	((SEGMENTS_AT_LEFT += 1))
 }
@@ -39,11 +41,12 @@ function __powerline_prompt_command {
 
 	## left prompt ##
 	for segment in $POWERLINE_PROMPT; do
-		local info="$(__powerline_${segment}_prompt)"
+		local info
+		info="$(__powerline_"${segment}"_prompt)"
 		[[ -n "${info}" ]] && __powerline_left_segment "${info}"
 	done
 
-	[[ "${last_status}" -ne 0 ]] && __powerline_left_segment $(__powerline_last_status_prompt ${last_status})
+	[[ "${last_status}" -ne 0 ]] && __powerline_left_segment "$(__powerline_last_status_prompt "${last_status}")"
 
 	if [[ -n "${LEFT_PROMPT}" ]] && [[ "${POWERLINE_COMPACT_AFTER_LAST_SEGMENT}" -eq 0 ]]; then
 		__powerline_left_last_segment_padding
diff --git a/themes/powerline-plain/powerline-plain.theme.bash b/themes/powerline-plain/powerline-plain.theme.bash
index 675715287d..2c0fd3eaa2 100644
--- a/themes/powerline-plain/powerline-plain.theme.bash
+++ b/themes/powerline-plain/powerline-plain.theme.bash
@@ -1,4 +1,5 @@
-#!/usr/bin/env bash
+# shellcheck shell=bash
+# shellcheck disable=SC2034
 
 . "$BASH_IT/themes/powerline-plain/powerline-plain.base.bash"