diff --git a/.gitignore b/.gitignore
new file mode 100644
index 00000000..8f6423fa
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+test-vm/.vagrant
diff --git a/README.md b/README.md
index 5427212f..2f71441c 100644
--- a/README.md
+++ b/README.md
@@ -19,6 +19,10 @@ like with a normal installation and default settings:
 - [Features](#features)
 - [Installation](#installation)
   - [Install Powerlevel9k](#install-powerlevel9k)
+    - [With plain ZSH](#with-plain-zsh)
+    - [With Oh-my-ZSH](#with-oh-my-zsh)
+    - [With Prezto](#with-prezto)
+    - [With antigen](#with-antigen)
   - [Install Powerline Fonts for Normal Configuration](#install-powerline-fonts-for-normal-configuration)
   - [Alternative Configuration: Über](#alternative-configuration-%C3%BCber)
   - [Alternative Configuration: Bare Bones](#alternative-configuration-bare-bones)
@@ -76,7 +80,16 @@ this theme:
 
 #### Install Powerlevel9k
 
-To install this theme, clone this repository into your Oh-My-Zsh `custom/themes`
+##### With plain ZSH
+
+If you use just a plain ZSH, just clone this repository and reference it in your `~/.zshrc`:
+
+    $ git clone https://github.com/bhilburn/powerlevel9k.git
+    $ echo 'source  powerlevel9k/powerlevel9k.zsh-theme' >> ~/.zshrc
+
+##### With Oh-my-ZSH
+
+To install this theme, clone this repository into your [Oh-my-Zsh](https://github.com/robbyrussell/oh-my-zsh) `custom/themes`
 directory.
 
     $ cd ~/.oh-my-zsh/custom
@@ -86,6 +99,25 @@ You then need to select this theme in your `~/.zshrc`:
 
     ZSH_THEME="powerlevel9k/powerlevel9k"
 
+##### With Prezto
+
+To install this theme, clone this repository into your [Prezto](https://github.com/sorin-ionescu/prezto) `prompt/external`
+directory.
+
+    $ cd ~.zprezto/modules/prompt/external
+    $ git clone https://github.com/bhilburn/powerlevel9k.git
+    $ ln -s powerlevel9k/powerlevel9k.zsh-theme ../functions/prompt_powerlevel9k_setup
+
+You then need to select this theme in your `~/.zpreztorc`:
+
+    zstyle ':prezto:module:prompt' theme 'powerlevel9k'
+
+##### With antigen
+
+If you prefer [antigen](https://github.com/zsh-users/antigen), just add it to your `~/.zshrc`:
+
+    $ echo 'antigen theme /vagrant_data powerlevel9k' >> ~/.zshrc
+    $ echo 'antigen apply' >> ~/.zshrc
 
 #### Install Powerline Fonts for Normal Configuration
 
@@ -338,3 +370,6 @@ Please submit your contribution as a Github pull-request.
 If you would like to contact me directly, you can find my e-mail address on my
 [Github profile page](https://github.com/bhilburn).
 
+### Testing
+
+Check out the [vagrant](https://www.vagrantup.com/) configuration in the [test-vm](test-vm) folder.
diff --git a/powerlevel9k.zsh-theme b/powerlevel9k.zsh-theme
index 8055ce05..1ebc31bb 100644
--- a/powerlevel9k.zsh-theme
+++ b/powerlevel9k.zsh-theme
@@ -169,8 +169,7 @@ esac
 # color scheme
 ################################################################
 
-local DEFAULT_COLOR DEFAULT_COLOR_INVERTED DEFAULT_COLOR_DARK
-if [[ $POWERLEVEL9K_COLOR_SCHEME == "light" ]]; then
+if [[ "$POWERLEVEL9K_COLOR_SCHEME" == "light" ]]; then
   DEFAULT_COLOR=white
   DEFAULT_COLOR_INVERTED=black
   DEFAULT_COLOR_DARK="252"
@@ -180,8 +179,8 @@ else
   DEFAULT_COLOR_DARK="236"
 fi
 
-local VCS_FOREGROUND_COLOR=$DEFAULT_COLOR
-local VCS_FOREGROUND_COLOR_DARK=$DEFAULT_COLOR_DARK
+VCS_FOREGROUND_COLOR=$DEFAULT_COLOR
+VCS_FOREGROUND_COLOR_DARK=$DEFAULT_COLOR_DARK
 
 # If user has defined custom colors for the `vcs` segment, override the defaults
 if [[ -n $POWERLEVEL9K_VCS_FOREGROUND ]]; then
@@ -198,13 +197,13 @@ fi
 setopt prompt_subst
 autoload -Uz vcs_info
 
-local VCS_WORKDIR_DIRTY=false
-local VCS_CHANGESET_PREFIX=''
+VCS_WORKDIR_DIRTY=false
+VCS_CHANGESET_PREFIX=''
 if [[ "$POWERLEVEL9K_SHOW_CHANGESET" == true ]]; then
   # Default: Just display the first 12 characters of our changeset-ID.
   local VCS_CHANGESET_HASH_LENGTH=12
-  if [[ -n $POWERLEVEL9K_CHANGESET_HASH_LENGTH ]]; then
-    VCS_CHANGESET_HASH_LENGTH=$POWERLEVEL9K_CHANGESET_HASH_LENGTH
+  if [[ -n "$POWERLEVEL9K_CHANGESET_HASH_LENGTH" ]]; then
+    VCS_CHANGESET_HASH_LENGTH="$POWERLEVEL9K_CHANGESET_HASH_LENGTH"
   fi
 
   VCS_CHANGESET_PREFIX="%F{$VCS_FOREGROUND_COLOR_DARK}$VCS_COMMIT_ICON%0.$VCS_CHANGESET_HASH_LENGTH""i%f"
@@ -213,7 +212,7 @@ fi
 zstyle ':vcs_info:*' enable git hg
 zstyle ':vcs_info:*' check-for-changes true
 
-local VCS_DEFAULT_FORMAT="$VCS_CHANGESET_PREFIX%F{$VCS_FOREGROUND_COLOR}%b%c%u%m%f"
+VCS_DEFAULT_FORMAT="$VCS_CHANGESET_PREFIX%F{$VCS_FOREGROUND_COLOR}%b%c%u%m%f"
 zstyle ':vcs_info:git:*' formats "%F{$VCS_FOREGROUND_COLOR}$VCS_GIT_ICON%f $VCS_DEFAULT_FORMAT" 
 zstyle ':vcs_info:hg:*' formats "%F{$VCS_FOREGROUND_COLOR}$VCS_HG_ICON%f $VCS_DEFAULT_FORMAT" 
 
@@ -315,11 +314,11 @@ right_prompt_segment() {
 prompt_vcs() {
   local vcs_prompt="${vcs_info_msg_0_}"
 
-  if [[ -n $vcs_prompt ]]; then
+  if [[ -n "$vcs_prompt" ]]; then
     if [[ "$VCS_WORKDIR_DIRTY" == true ]]; then
-      $1_prompt_segment $0_MODIFIED yellow $DEFAULT_COLOR
+      $1_prompt_segment "$0_MODIFIED" "yellow" "$DEFAULT_COLOR"
     else
-      $1_prompt_segment $0 green $DEFAULT_COLOR
+      $1_prompt_segment "$0" "green" "$DEFAULT_COLOR"
     fi
 
     echo -n "%F{$VCS_FOREGROUND_COLOR}%f$vcs_prompt "
@@ -372,7 +371,7 @@ function +vi-git-tagname() {
     local tag
 
     tag=$(git describe --tags --exact-match HEAD 2>/dev/null)
-    [[ -n ${tag} ]] && hook_com[branch]=" %F{$VCS_FOREGROUND_COLOR}$VCS_TAG_ICON${tag}%f"
+    [[ -n "${tag}" ]] && hook_com[branch]=" %F{$VCS_FOREGROUND_COLOR}$VCS_TAG_ICON${tag}%f"
 }
 
 # Show count of stashed changes
@@ -399,7 +398,7 @@ function +vi-hg-bookmarks() {
 }
 
 function +vi-vcs-detect-changes() {
-  if [[ -n ${hook_com[staged]} ]] || [[ -n ${hook_com[unstaged]} ]]; then
+  if [[ -n "${hook_com[staged]}" ]] || [[ -n "${hook_com[unstaged]}" ]]; then
     VCS_WORKDIR_DIRTY=true
   else
     VCS_WORKDIR_DIRTY=false
@@ -417,10 +416,10 @@ CURRENT_BG='NONE'
 
 # AWS Profile
 prompt_aws() {
-  local aws_profile=$AWS_DEFAULT_PROFILE
-  if [[ -n $aws_profile ]]; 
+  local aws_profile="$AWS_DEFAULT_PROFILE"
+  if [[ -n "$aws_profile" ]]; 
   then
-    $1_prompt_segment $0 red white "$AWS_ICON $aws_profile"
+    $1_prompt_segment "$0" red white "$AWS_ICON $aws_profile"
   fi
 }
 
@@ -428,18 +427,18 @@ prompt_aws() {
 # Note that if $DEFAULT_USER is not set, this prompt segment will always print
 prompt_context() {
   if [[ "$USER" != "$DEFAULT_USER" || -n "$SSH_CLIENT" ]]; then
-    $1_prompt_segment $0 $DEFAULT_COLOR "011" "%(!.%{%F{yellow}%}.)$USER@%m"
+    $1_prompt_segment "$0" "$DEFAULT_COLOR" "011" "%(!.%{%F{yellow}%}.)$USER@%m"
   fi
 }
 
 # Dir: current working directory
 prompt_dir() {
-  $1_prompt_segment $0 blue $DEFAULT_COLOR '%~'
+  $1_prompt_segment "$0" "blue" "$DEFAULT_COLOR" '%~'
 }
 
 # Command number (in local history)
 prompt_history() {
-  $1_prompt_segment $0 "244" $DEFAULT_COLOR '%h'
+  $1_prompt_segment "$0" "244" "$DEFAULT_COLOR" '%h'
 }
 
 # Right Status: (return code, root status, background jobs)
@@ -449,24 +448,24 @@ prompt_longstatus() {
   local symbols bg
   symbols=()
 
-  if [[ $RETVAL -ne 0 ]]; then
-    symbols+="%{%F{"226"}%}%? ↵"
+  if [[ "$RETVAL" -ne 0 ]]; then
+    symbols+="%F{226}%? ↵"
     bg="009"
   else
     symbols+="%{%F{"046"}%}$OK_ICON"
     bg="008"
   fi
 
-  [[ $UID -eq 0 ]] && symbols+="%{%F{yellow}%} $ROOT_ICON"
+  [[ "$UID" -eq 0 ]] && symbols+="%{%F{yellow}%} $ROOT_ICON"
   [[ $(jobs -l | wc -l) -gt 0 ]] && symbols+="%{%F{cyan}%}$BACKGROUND_JOBS_ICON"
 
-  [[ -n "$symbols" ]] && $1_prompt_segment $0 $bg $DEFAULT_COLOR "$symbols"
+  [[ -n "$symbols" ]] && $1_prompt_segment "$0" "$bg" "$DEFAULT_COLOR" "$symbols"
 }
 
 # rbenv information
 prompt_rbenv() {
   if [[ -n "$RBENV_VERSION" ]]; then
-    $1_prompt_segment $0 red $DEFAULT_COLOR "$RBENV_VERSION"
+    $1_prompt_segment "$0" "red" "$DEFAULT_COLOR" "$RBENV_VERSION"
   fi
 }
 
@@ -476,7 +475,7 @@ prompt_rspec_stats() {
     local code_amount=$(ls -1 app/**/*.rb | wc -l)
     local tests_amount=$(ls -1 spec/**/*.rb | wc -l)
 
-    build_test_stats $1 $0 $code_amount $tests_amount "RSpec $TEST_ICON"
+    build_test_stats "$1" $0 "$code_amount" $tests_amount "RSpec $TEST_ICON"
   fi
 }
 
@@ -485,7 +484,7 @@ prompt_rvm() {
   local rvm_prompt
   rvm_prompt=`rvm-prompt`
   if [ "$rvm_prompt" != "" ]; then
-    $1_prompt_segment $0 "240" $DEFAULT_COLOR "$rvm_prompt $RUBY_ICON "
+    $1_prompt_segment "$0" "240" "$DEFAULT_COLOR" "$rvm_prompt $RUBY_ICON "
   fi
 }
 
@@ -494,11 +493,11 @@ prompt_rvm() {
 prompt_status() {
   local symbols
   symbols=()
-  [[ $RETVAL -ne 0 ]] && symbols+="%{%F{red}%}$FAIL_ICON"
-  [[ $UID -eq 0 ]] && symbols+="%{%F{yellow}%} $ROOT_ICON"
+  [[ "$RETVAL" -ne 0 ]] && symbols+="%{%F{red}%}$FAIL_ICON"
+  [[ "$UID" -eq 0 ]] && symbols+="%{%F{yellow}%} $ROOT_ICON"
   [[ $(jobs -l | wc -l) -gt 0 ]] && symbols+="%{%F{cyan}%}$BACKGROUND_JOBS_ICON"
 
-  [[ -n "$symbols" ]] && $1_prompt_segment $0 $DEFAULT_COLOR default "$symbols"
+  [[ -n "$symbols" ]] && $1_prompt_segment "$0" "$DEFAULT_COLOR" "default" "$symbols"
 }
 
 # Symfony2-PHPUnit test ratio
@@ -507,33 +506,33 @@ prompt_symfony2_tests() {
     local code_amount=$(ls -1 src/**/*.php | grep -v Tests | wc -l)
     local tests_amount=$(ls -1 src/**/*.php | grep Tests | wc -l)
 
-    build_test_stats $1 $0 $code_amount $tests_amount "SF2 $TEST_ICON"
+    build_test_stats "$1" "$0" "$code_amount" "$tests_amount" "SF2 $TEST_ICON"
   fi
 }
 
 # Show a ratio of tests vs code
 build_test_stats() {
-  local code_amount=$3
-  local tests_amount=$4+0.00001
-  local headline=$5
+  local code_amount="$3"
+  local tests_amount="$4"+0.00001
+  local headline="$5"
 
   # Set float precision to 2 digits:
   typeset -F 2 ratio
   local ratio=$(( (tests_amount/code_amount) * 100 ))
 
-  [[ ratio -ge 0.75 ]] && $1_prompt_segment ${2}_GOOD cyan $DEFAULT_COLOR "$headline: $ratio%%"
-  [[ ratio -ge 0.5 && ratio -lt 0.75 ]] && $1_prompt_segment $2_AVG yellow $DEFAULT_COLOR "$headline: $ratio%%"
-  [[ ratio -lt 0.5 ]] && $1_prompt_segment $2_BAD red $DEFAULT_COLOR "$headline: $ratio%%"
+  [[ ratio -ge 0.75 ]] && $1_prompt_segment "${2}_GOOD" "cyan" "$DEFAULT_COLOR" "$headline: $ratio%%"
+  [[ ratio -ge 0.5 && ratio -lt 0.75 ]] && $1_prompt_segment "$2_AVG" "yellow" "$DEFAULT_COLOR" "$headline: $ratio%%"
+  [[ ratio -lt 0.5 ]] && $1_prompt_segment "$2_BAD" "red" "$DEFAULT_COLOR" "$headline: $ratio%%"
 }
 
 # System time
 prompt_time() {
-  local time_format='%D{%H:%M:%S}'
-  if [[ -n $POWERLEVEL9K_TIME_FORMAT ]]; then
-    time_format=$POWERLEVEL9K_TIME_FORMAT
+  local time_format="%D{%H:%M:%S}"
+  if [[ -n "$POWERLEVEL9K_TIME_FORMAT" ]]; then
+    time_format="$POWERLEVEL9K_TIME_FORMAT"
   fi
 
-  $1_prompt_segment $0 $DEFAULT_COLOR_INVERTED $DEFAULT_COLOR $time_format
+  $1_prompt_segment "$0" "$DEFAULT_COLOR_INVERTED" "$DEFAULT_COLOR" "$time_format"
 }
 
 # Virtualenv: current working virtualenv
@@ -541,8 +540,8 @@ prompt_time() {
 # https://virtualenv.pypa.io/en/latest/
 prompt_virtualenv() {
   local virtualenv_path="$VIRTUAL_ENV"
-  if [[ -n $virtualenv_path && -n $VIRTUAL_ENV_DISABLE_PROMPT ]]; then
-    $1_prompt_segment $0 blue $DEFAULT_COLOR "(`basename $virtualenv_path`)"
+  if [[ -n "$virtualenv_path" && -n "$VIRTUAL_ENV_DISABLE_PROMPT" ]]; then
+    $1_prompt_segment "$0" "blue" "$DEFAULT_COLOR" "(`basename $virtualenv_path`)"
   fi
 }
 
@@ -552,7 +551,7 @@ prompt_virtualenv() {
 
 # Main prompt
 build_left_prompt() {
-  if [[ ${#POWERLEVEL9K_LEFT_PROMPT_ELEMENTS} == 0 ]]; then
+  if [[ "${#POWERLEVEL9K_LEFT_PROMPT_ELEMENTS}" == 0 ]]; then
     POWERLEVEL9K_LEFT_PROMPT_ELEMENTS=(context dir rbenv vcs)
   fi
 
@@ -567,7 +566,7 @@ build_left_prompt() {
 build_right_prompt() {
   RETVAL=$?
 
-  if [[ ${#POWERLEVEL9K_RIGHT_PROMPT_ELEMENTS} == 0 ]]; then
+  if [[ "${#POWERLEVEL9K_RIGHT_PROMPT_ELEMENTS}" == 0 ]]; then
     POWERLEVEL9K_RIGHT_PROMPT_ELEMENTS=(longstatus history time)
   fi
 
@@ -576,26 +575,43 @@ build_right_prompt() {
   done
 }
 
-precmd() {
+prompt_powerlevel9k_precmd() {
   vcs_info
 
   # Add a static hook to examine staged/unstaged changes.
   vcs_info_hookadd set-message vcs-detect-changes
 }
 
-if [[ "$POWERLEVEL9K_PROMPT_ON_NEWLINE" == true ]]; then
-  PROMPT='╭─%{%f%b%k%}$(build_left_prompt) 
-╰─ '
-  # The right prompt should be on the same line as the first line of the left
-  # prompt.  To do so, there is just a quite ugly workaround: Before zsh draws
-  # the RPROMPT, we advise it, to go one line up. At the end of RPROMPT, we
-  # advise it to go one line down. See:
-  # http://superuser.com/questions/357107/zsh-right-justify-in-ps1
-  RPROMPT_PREFIX='%{'$'\e[1A''%}' # one line up
-  RPROMPT_SUFFIX='%{'$'\e[1B''%}' # one line down
-else
-  PROMPT='%{%f%b%k%}$(build_left_prompt)'
-  RPROMPT_PREFIX=''
-  RPROMPT_SUFFIX=''
-fi
-RPROMPT=$RPROMPT_PREFIX'%{%f%b%k%}$(build_right_prompt)%{$reset_color%}'$RPROMPT_SUFFIX
+powerlevel9k_init() {
+  setopt LOCAL_OPTIONS
+  unsetopt XTRACE KSH_ARRAYS
+  prompt_opts=(cr percent subst)
+
+  # initialize colors
+  autoload -U colors && colors
+
+  # initialize VCS
+  autoload -Uz add-zsh-hook
+
+  add-zsh-hook precmd prompt_powerlevel9k_precmd
+
+  if [[ "$POWERLEVEL9K_PROMPT_ON_NEWLINE" == true ]]; then
+    PROMPT="╭─%{%f%b%k%}"'$(build_left_prompt)'" 
+╰─ "
+    # The right prompt should be on the same line as the first line of the left
+    # prompt.  To do so, there is just a quite ugly workaround: Before zsh draws
+    # the RPROMPT, we advise it, to go one line up. At the end of RPROMPT, we
+    # advise it to go one line down. See:
+    # http://superuser.com/questions/357107/zsh-right-justify-in-ps1
+    RPROMPT_PREFIX='%{'$'\e[1A''%}' # one line up
+    RPROMPT_SUFFIX='%{'$'\e[1B''%}' # one line down
+  else
+    PROMPT="%{%f%b%k%}"'$(build_left_prompt)'
+    RPROMPT_PREFIX=''
+    RPROMPT_SUFFIX=''
+  fi
+  RPROMPT=$RPROMPT_PREFIX"%{%f%b%k%}"'$(build_right_prompt)'"%{$reset_color%}"$RPROMPT_SUFFIX
+
+}
+
+powerlevel9k_init "$@"