diff --git a/aliases/available/apt.aliases.bash b/aliases/available/apt.aliases.bash
index 2f444931..b7ef274c 100644
--- a/aliases/available/apt.aliases.bash
+++ b/aliases/available/apt.aliases.bash
@@ -1,4 +1,4 @@
-#!/bin/bash
+# shellcheck shell=bash
 #
 # -binaryanomaly
 
@@ -8,7 +8,8 @@ about-alias 'Apt and dpkg aliases for Ubuntu and Debian distros.'
 # set apt aliases
 function _set_pkg_aliases()
 {
-	if [ -x $(which apt) ]; then
+	if _command_exists apt
+	then
 		alias apts='apt-cache search'
 		alias aptshow='apt-cache show'
 		alias aptinst='sudo apt-get install -V'
diff --git a/aliases/available/curl.aliases.bash b/aliases/available/curl.aliases.bash
index 3ced1bb5..a6b2b344 100644
--- a/aliases/available/curl.aliases.bash
+++ b/aliases/available/curl.aliases.bash
@@ -6,7 +6,8 @@ about-alias 'Curl aliases for convenience.'
 # set apt aliases
 function _set_pkg_aliases()
 {
-	if [ -x $(which curl) ]; then
+	if _command_exists curl
+	then
 		# follow redirects
                 alias cl='curl -L'
                 # follow redirects, download as original name
diff --git a/aliases/available/general.aliases.bash b/aliases/available/general.aliases.bash
index 0c7bcd9d..61ebe538 100644
--- a/aliases/available/general.aliases.bash
+++ b/aliases/available/general.aliases.bash
@@ -30,7 +30,7 @@ then
   alias grep='grep --color=auto'
 fi
 
-if which gshuf &> /dev/null
+if _command_exists gshuf
 then
   alias shuf=gshuf
 fi
@@ -65,7 +65,7 @@ alias -- -='cd -'        # Go back
 alias h='history'
 
 # Tree
-if [ ! -x "$(which tree 2>/dev/null)" ]
+if ! _command_exists tree
 then
   alias tree="find . -print | sed -e 's;[^/]*/;|____;g;s;____|; |;g'"
 fi
diff --git a/aliases/available/vim.aliases.bash b/aliases/available/vim.aliases.bash
index d19057d0..d5dcdc54 100644
--- a/aliases/available/vim.aliases.bash
+++ b/aliases/available/vim.aliases.bash
@@ -2,11 +2,7 @@
 cite 'about-alias'
 about-alias 'vim abbreviations'
 
-VIM=$(command -v vim)
-GVIM=$(command -v gvim)
-MVIM=$(command -v mvim)
-
-if [[ -n $VIM ]]; then
+if _command_exists vim; then
 	alias v='$VIM'
 	# open the vim help in fullscreen incorporated from
 	# https://stackoverflow.com/a/4687513
@@ -17,9 +13,9 @@ fi
 # http://stackoverflow.com/questions/936501/let-gvim-always-run-a-single-instancek
 case $OSTYPE in
 	darwin*)
-		[[ -n $MVIM ]] && function mvimt { command mvim --remote-tab-silent "$@" || command mvim "$@"; }
+		_command_exists mvim && function mvimt { command mvim --remote-tab-silent "$@" || command mvim "$@"; }
 		;;
 	*)
-		[[ -n $GVIM ]] && function gvimt { command gvim --remote-tab-silent "$@" || command gvim "$@"; }
+		_command_exists gvim && function gvimt { command gvim --remote-tab-silent "$@" || command gvim "$@"; }
 		;;
 esac
diff --git a/bash_it.sh b/bash_it.sh
index 679ffdaf..215c33c7 100755
--- a/bash_it.sh
+++ b/bash_it.sh
@@ -145,7 +145,7 @@ if [ -e "$HOME/.jekyllconfig" ]; then
 fi
 
 # BASH_IT_RELOAD_LEGACY is set.
-if ! command -v reload &> /dev/null && [ -n "${BASH_IT_RELOAD_LEGACY:-}" ]; then
+if ! _command_exists reload && [[ -n "${BASH_IT_RELOAD_LEGACY:-}" ]]; then
 	case $OSTYPE in
 		darwin*)
 			alias reload='source ~/.bash_profile'
diff --git a/clean_files.txt b/clean_files.txt
index b8fcee4f..2242ef5e 100644
--- a/clean_files.txt
+++ b/clean_files.txt
@@ -77,8 +77,10 @@ completion/available/wpscan.completion.bash
 # plugins
 #
 plugins/available/alias-completion.plugin.bash
+plugins/available/autojump.plugin.bash
 plugins/available/basher.plugin.bash
 plugins/available/cmd-returned-notify.plugin.bash
+plugins/available/direnv.plugin.bash
 plugins/available/docker-machine.plugin.bash
 plugins/available/git.plugin.bash
 plugins/available/go.plugin.bash
@@ -86,6 +88,14 @@ plugins/available/goenv.plugin.bash
 plugins/available/history-search.plugin.bash
 plugins/available/history-substring-search.plugin.bash
 plugins/available/history.plugin.bash
+plugins/available/hub.plugin.bash
+plugins/available/jump.plugin.bash
+plugins/available/node.plugin.bash
+plugins/available/nodenv.plugin.bash
+plugins/available/plenv.plugin.bash
+plugins/available/pyenv.plugin.bash
+plugins/available/rbenv.plugin.bash
+plugins/available/textmate.plugin.bash
 plugins/available/xterm.plugin.bash
 
 # tests
diff --git a/completion/available/awscli.completion.bash b/completion/available/awscli.completion.bash
index 530bdd27..a3041837 100644
--- a/completion/available/awscli.completion.bash
+++ b/completion/available/awscli.completion.bash
@@ -1 +1,6 @@
-[[ -x "$(which aws_completer)" ]] && complete -C "$(which aws_completer)" aws
+# shellcheck shell=bash
+
+if _command_exists aws_completer
+then
+	complete -C "$(command -v aws_completer)" aws
+fi
diff --git a/completion/available/consul.completion.bash b/completion/available/consul.completion.bash
index 3697ffc5..511cf372 100644
--- a/completion/available/consul.completion.bash
+++ b/completion/available/consul.completion.bash
@@ -3,5 +3,5 @@ cite "about-completion"
 about-completion "Hashicorp consul completion"
 
 if _command_exists consul; then
-	complete -C "$(which consul)" consul
+	complete -C "$(command -v consul)" consul
 fi
diff --git a/completion/available/docker-compose.completion.bash b/completion/available/docker-compose.completion.bash
old mode 100644
new mode 100755
index bf2c13fb..1102f5d9
--- a/completion/available/docker-compose.completion.bash
+++ b/completion/available/docker-compose.completion.bash
@@ -676,7 +676,7 @@ _docker_compose() {
 	done
 
 	local completions_func=_docker_compose_${command//-/_}
-	declare -F $completions_func >/dev/null && $completions_func
+	_is_function $completions_func && $completions_func
 
 	eval "$previous_extglob_setting"
 	return 0
diff --git a/completion/available/git_flow.completion.bash b/completion/available/git_flow.completion.bash
index 04f20ccd..7bfc9ef4 100644
--- a/completion/available/git_flow.completion.bash
+++ b/completion/available/git_flow.completion.bash
@@ -172,6 +172,7 @@ __git_flow_list_hotfixes ()
 }
 
 # temporarily wrap __git_find_on_cmdline() for backwards compatibility
-if [ -z "`type -t __git_find_subcommand`" ]; then
+if ! _command_exists __git_find_subcommand
+then
 	alias __git_find_subcommand=__git_find_on_cmdline
 fi
diff --git a/completion/available/git_flow_avh.completion.bash b/completion/available/git_flow_avh.completion.bash
index 0b73a0be..abb51bf8 100644
--- a/completion/available/git_flow_avh.completion.bash
+++ b/completion/available/git_flow_avh.completion.bash
@@ -505,6 +505,7 @@ __git_flow_list_branches ()
 }
 
 # alias __git_find_on_cmdline for backwards compatibility
-if [ -z "`type -t __git_find_on_cmdline`" ]; then
+if ! _command_exists __git_find_on_cmdline
+then
 	alias __git_find_on_cmdline=__git_find_subcommand
 fi
diff --git a/completion/available/gradle.completion.bash b/completion/available/gradle.completion.bash
index 6ec8c697..786450a6 100644
--- a/completion/available/gradle.completion.bash
+++ b/completion/available/gradle.completion.bash
@@ -58,9 +58,9 @@ __gradle-set-cache-name() {
 
 __gradle-set-files-checksum() {
     # Cache MD5 sum of all Gradle scripts and modified timestamps
-    if builtin command -v md5 > /dev/null; then
+    if _command_exists md5; then
         gradle_files_checksum=$(md5 -q -s "$(cat "$cache_dir/$cache_name" | xargs ls -o 2>/dev/null)")
-    elif builtin command -v md5sum > /dev/null; then
+    elif _command_exists md5sum; then
         gradle_files_checksum=$(cat "$cache_dir/$cache_name" | xargs ls -o 2>/dev/null | md5sum | awk '{print $1}')
     else
         echo "Cannot generate completions as neither md5 nor md5sum exist on \$PATH"
diff --git a/completion/available/hub.completion.bash b/completion/available/hub.completion.bash
index 74c530a8..67a5e29b 100644
--- a/completion/available/hub.completion.bash
+++ b/completion/available/hub.completion.bash
@@ -23,12 +23,12 @@
 # WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 
 # If there is no git tab completion, but we have the _completion loader try to load it
-if ! declare -F _git > /dev/null && declare -F _completion_loader > /dev/null; then
+if ! _is_function _git && _is_function _completion_loader; then
   _completion_loader git
 fi
 
 # Check that git tab completion is available and we haven't already set up completion
-if declare -F _git > /dev/null && ! declare -F __git_list_all_commands_without_hub > /dev/null; then
+if _is_function _git && ! _is_function __git_list_all_commands_without_hub; then
   # Duplicate and rename the 'list_all_commands' function
   eval "$(declare -f __git_list_all_commands | \
         sed 's/__git_list_all_commands/__git_list_all_commands_without_hub/')"
diff --git a/completion/available/laravel.completion.bash b/completion/available/laravel.completion.bash
index 7bd6f223..9298a7bf 100644
--- a/completion/available/laravel.completion.bash
+++ b/completion/available/laravel.completion.bash
@@ -1,7 +1,9 @@
 #!/usr/bin/bash
 
-if command -v laravel > /dev/null; then
-    __laravel_completion()  {
+if _command_exists laravel
+then
+    function __laravel_completion()
+	{
         local OPTS=("-h --help -q --quiet --ansi --no-ansi -n --no-interaction -v -vv -vvv --verbose help list new")
         COMPREPLY=()
         for _opt_ in ${OPTS[@]}; do
@@ -9,7 +11,7 @@ if command -v laravel > /dev/null; then
                 COMPREPLY+=("$_opt_")
             fi
         done
-    }
+	}
 
     complete -F __laravel_completion laravel
 fi
diff --git a/completion/available/pew.completion.bash b/completion/available/pew.completion.bash
index 73d62e39..04e67ecb 100644
--- a/completion/available/pew.completion.bash
+++ b/completion/available/pew.completion.bash
@@ -1 +1,6 @@
-[[ -x "$(which pew)" ]] && source "$(pew shell_config)"
+# shellcheck shell=bash
+
+if _command_exists pew
+then
+	source "$(pew shell_config)"
+fi
diff --git a/completion/available/sqlmap.completion.bash b/completion/available/sqlmap.completion.bash
index 16addf85..213dd817 100644
--- a/completion/available/sqlmap.completion.bash
+++ b/completion/available/sqlmap.completion.bash
@@ -1,21 +1,22 @@
-#!/bin/bash
+# shellcheck shell=bash
 
 # ---------------------------------------------------------------------------+
 #                                                                            |
-# Thanks to Alexander Korznikov                                                                 |
+# Thanks to Alexander Korznikov                                              |
 # http://www.korznikov.com/2014/12/bash-tab-completion-for-awesome-tool.html |
 #                                                                            |
 # ---------------------------------------------------------------------------+
 
-if command -v sqlmap > /dev/null; then
+if _command_exists sqlmap
+then
 
-    _sqlmap()
+    function _sqlmap()
     {
         local cur prev
 
         COMPREPLY=()
-        cur=$(_get_cword)
-        prev=$(_get_pword)
+        cur="$(_get_cword)"
+        prev="$(_get_pword)"
 
         case $prev in
 
@@ -143,7 +144,7 @@ if command -v sqlmap > /dev/null; then
         --mobile --page-rank --purge-output --smart \
         --sqlmap-shell --wizard '
         COMPREPLY=( $( \
-            (while read -d ' ' i; do
+		(while read -d ' ' i; do
                 [[ -z "$i" || "${onlyonce/ ${i%% *} / }" == "$onlyonce" ]] &&
                 continue
                 # flatten array with spaces on either side,
@@ -152,7 +153,7 @@ if command -v sqlmap > /dev/null; then
                 COMPREPLY=" ${COMPREPLY[@]} "
                 # remove word from list of completions
                 COMPREPLY=( ${COMPREPLY/ ${i%% *} / } )
-                done
+			done
                 printf '%s ' "${COMPREPLY[@]}") <<<"${COMP_WORDS[@]}"
             ) )
 
diff --git a/completion/available/travis.completion.bash b/completion/available/travis.completion.bash
index 28d599aa..49d8f2cc 100644
--- a/completion/available/travis.completion.bash
+++ b/completion/available/travis.completion.bash
@@ -1,5 +1,10 @@
-if [[ -x "$(which travis)" ]]; then
-  __TRAVIS_COMPLETION_SCRIPT="${TRAVIS_CONFIG_PATH:-${HOME}/.travis}/travis.sh"
-  [[ -f "${__TRAVIS_COMPLETION_SCRIPT}" ]] && source "${__TRAVIS_COMPLETION_SCRIPT}"
+# shellcheck shell=bash
+
+if _command_exists travis
+then
+  if [[ -s "${__TRAVIS_COMPLETION_SCRIPT:=${TRAVIS_CONFIG_PATH:-${HOME}/.travis}/travis.sh}" ]]
+	then
+		source "${__TRAVIS_COMPLETION_SCRIPT}"
+	fi
   unset __TRAVIS_COMPLETION_SCRIPT
 fi
diff --git a/completion/available/wpscan.completion.bash b/completion/available/wpscan.completion.bash
index 5d2e2daa..8891ab7f 100644
--- a/completion/available/wpscan.completion.bash
+++ b/completion/available/wpscan.completion.bash
@@ -1,7 +1,7 @@
 # shellcheck shell=bash
 
-if command -v wpscan > /dev/null; then
-	__wpscan_completion() {
+if _command_exists wpscan; then
+	function __wpscan_completion() {
 		local OPTS=("--help --hh --version --url --ignore-main-redirect --verbose --output --format --detection-mode --scope --headers --user-agent --vhost --random-user-agent --user-agents-list --http-auth --max-threads --throttle --request-timeout --connect-timeout --disable-tlc-checks --proxy --proxy-auth --cookie-string --cookie-jar --cache-ttl --clear-cache --server --cache-dir --update --no-update --wp-content-dir --wp-plugins-dir --wp-version-detection --main-theme-detection --enumerate --exclude-content-based --plugins-list --plugins-detection --plugins-version-all --plugins-version-detection --themes-list --themes-detection --themes-version-all --themes-version-detection --timthumbs-list --timthumbs-detection --config-backups-list --config-backups-detection --db-exports-list --db-exports-detection --medias-detection --users-list --users-detection --passwords --usernames --multicall-max-passwords --password-attack --stealthy")
 		COMPREPLY=()
 		for _opt_ in "${OPTS[@]}"; do
diff --git a/lib/helpers.bash b/lib/helpers.bash
old mode 100644
new mode 100755
index 61705a04..fbc6aa88
--- a/lib/helpers.bash
+++ b/lib/helpers.bash
@@ -23,7 +23,13 @@ function _command_exists ()
   _example '$ _command_exists ls && echo exists'
   _group 'lib'
   local msg="${2:-Command '$1' does not exist!}"
-  type "$1" &> /dev/null || (_log_warning "$msg" && return 1) ;
+  if type -t "$1" &> /dev/null
+  then
+	  return 0
+  else
+	  _log_warning "$msg"
+	  return 1
+  fi
 }
 
 function _binary_exists ()
@@ -34,7 +40,13 @@ function _binary_exists ()
   _example '$ _binary_exists ls && echo exists'
   _group 'lib'
   local msg="${2:-Binary '$1' does not exist!}"
-  type -P "$1" &> /dev/null || (_log_warning "$msg" && return 1) ;
+  if type -P "$1" &> /dev/null
+  then
+	return 0
+  else
+	_log_warning "$msg"
+	return 1
+  fi
 }
 
 function _completion_exists ()
diff --git a/plugins/available/autojump.plugin.bash b/plugins/available/autojump.plugin.bash
index 7e6df7fc..dc8fbbb4 100644
--- a/plugins/available/autojump.plugin.bash
+++ b/plugins/available/autojump.plugin.bash
@@ -1,12 +1,15 @@
+# shellcheck shell=bash
 cite about-plugin
 about-plugin 'Autojump configuration, see https://github.com/wting/autojump for more details'
 
 # Only supports the Homebrew variant, Debian and Arch at the moment.
 # Feel free to provide a PR to support other install locations
 if _bash_it_homebrew_check && [[ -s "${BASH_IT_HOMEBREW_PREFIX}/etc/profile.d/autojump.sh" ]]; then
-  . "${BASH_IT_HOMEBREW_PREFIX}/etc/profile.d/autojump.sh"
-elif command -v dpkg &>/dev/null && dpkg -s autojump &>/dev/null ; then
-  . "$(dpkg-query -S autojump.sh | cut -d' ' -f2)"
-elif command -v pacman &>/dev/null && pacman -Q autojump &>/dev/null ; then
-  . "$(pacman -Ql autojump | grep autojump.sh | cut -d' ' -f2)"
+	source "${BASH_IT_HOMEBREW_PREFIX}/etc/profile.d/autojump.sh"
+elif _command_exists dpkg && dpkg -s autojump &> /dev/null; then
+	# shellcheck disable=SC1090
+	source "$(dpkg-query -S autojump.sh | cut -d' ' -f2)"
+elif _command_exists pacman && pacman -Q autojump &> /dev/null; then
+	# shellcheck disable=SC1090
+	source "$(pacman -Ql autojump | grep autojump.sh | cut -d' ' -f2)"
 fi
diff --git a/plugins/available/base.plugin.bash b/plugins/available/base.plugin.bash
index 8499a2df..b0899ce9 100644
--- a/plugins/available/base.plugin.bash
+++ b/plugins/available/base.plugin.bash
@@ -5,10 +5,10 @@ function ips ()
 {
     about 'display all ip addresses for this host'
     group 'base'
-    if command -v ifconfig &>/dev/null
+    if _command_exists ifconfig
     then
         ifconfig | awk '/inet /{ gsub(/addr:/, ""); print $2 }'
-    elif command -v ip &>/dev/null
+    elif _command_exists ip
     then
         ip addr | grep -oP 'inet \K[\d.]+'
     else
@@ -70,7 +70,7 @@ function passgen ()
 
 # Create alias pass to passgen when pass isn't installed or
 # BASH_IT_LEGACY_PASS is true.
-if ! command -v pass &>/dev/null || [[ "${BASH_IT_LEGACY_PASS:-}" = true ]]
+if ! _command_exists pass || [[ "${BASH_IT_LEGACY_PASS:-}" = true ]]
 then
   alias pass=passgen
 fi
@@ -81,7 +81,7 @@ function pmdown ()
     param '1: markdown file'
     example '$ pmdown README.md'
     group 'base'
-    if command -v markdown &>/dev/null
+    if _command_exists markdown
     then
       markdown $1 | browser
     else
diff --git a/plugins/available/direnv.plugin.bash b/plugins/available/direnv.plugin.bash
index 5fd564f5..62788600 100644
--- a/plugins/available/direnv.plugin.bash
+++ b/plugins/available/direnv.plugin.bash
@@ -1,4 +1,7 @@
+# shellcheck shell=bash
 cite about-plugin
 about-plugin 'load direnv, if you are using it: https://direnv.net/'
 
-[ -x "$(which direnv)" ] && eval "$(direnv hook bash)"
+if _command_exists direnv; then
+	eval "$(direnv hook bash)"
+fi
diff --git a/plugins/available/hub.plugin.bash b/plugins/available/hub.plugin.bash
index 0a67a7af..e9a8cbab 100644
--- a/plugins/available/hub.plugin.bash
+++ b/plugins/available/hub.plugin.bash
@@ -1,4 +1,7 @@
+# shellcheck shell=bash
 cite about-plugin
 about-plugin 'load hub, if you are using it'
 
-command -v hub &> /dev/null && eval "$(hub alias -s)"
+if _command_exists hub; then
+	eval "$(hub alias -s)"
+fi
diff --git a/plugins/available/jump.plugin.bash b/plugins/available/jump.plugin.bash
index 26d6467d..1713d1b7 100644
--- a/plugins/available/jump.plugin.bash
+++ b/plugins/available/jump.plugin.bash
@@ -1,9 +1,12 @@
+# shellcheck shell=bash
+# shellcheck disable=SC2016
 cite about-plugin
 about-plugin 'initialize jump (see https://github.com/gsamokovarov/jump). Add `export JUMP_OPTS=("--bind=z")` to change keybinding'
 
-__init_jump() {
-  command -v jump &> /dev/null || return
-  eval "$(jump shell bash "${JUMP_OPTS[@]}")"
+function __init_jump() {
+	if _command_exists jump; then
+		eval "$(jump shell bash "${JUMP_OPTS[@]}")"
+	fi
 }
 
 __init_jump
diff --git a/plugins/available/node.plugin.bash b/plugins/available/node.plugin.bash
index 65df3da3..8bf876df 100644
--- a/plugins/available/node.plugin.bash
+++ b/plugins/available/node.plugin.bash
@@ -1,13 +1,14 @@
+# shellcheck shell=bash
 cite about-plugin
 about-plugin 'Node.js helper functions'
 
+# Check that we have npm
+_command_exists npm || return
+
 # Ensure local modules are preferred in PATH
 pathmunge "./node_modules/.bin" "after"
 
-# Check that we have npm
-out=$(command -v npm 2>&1) || return
-
 # If not using nodenv, ensure global modules are in PATH
-if [[ ! $out == *"nodenv/shims"* ]] ; then
-  pathmunge "$(npm config get prefix)/bin" "after"
+if [[ ! "$(type -p npm)" == *"nodenv/shims"* ]]; then
+	pathmunge "$(npm config get prefix)/bin" "after"
 fi
diff --git a/plugins/available/nodenv.plugin.bash b/plugins/available/nodenv.plugin.bash
index 1bbe7fbd..262a57c3 100644
--- a/plugins/available/nodenv.plugin.bash
+++ b/plugins/available/nodenv.plugin.bash
@@ -1,7 +1,10 @@
+# shellcheck shell=bash
 cite about-plugin
 about-plugin 'load nodenv, if you are using it'
 
 export NODENV_ROOT="$HOME/.nodenv"
 pathmunge "$NODENV_ROOT/bin"
 
-[[ `which nodenv` ]] && eval "$(nodenv init - bash)"
+if _command_exists nodenv; then
+	eval "$(nodenv init - bash)"
+fi
diff --git a/plugins/available/nvm.plugin.bash b/plugins/available/nvm.plugin.bash
index 87dce644..0e6da5d8 100644
--- a/plugins/available/nvm.plugin.bash
+++ b/plugins/available/nvm.plugin.bash
@@ -1,22 +1,23 @@
-# Bash-it no longer bundles nvm, as this was quickly becoming outdated.
+# shellcheck shell=bash
 #
 # BASH_IT_LOAD_PRIORITY: 225
 #
+# Bash-it no longer bundles nvm, as this was quickly becoming outdated.
 # Please install nvm from https://github.com/creationix/nvm.git if you want to use it.
 
 cite about-plugin
 about-plugin 'node version manager configuration'
 
-export NVM_DIR=${NVM_DIR:-$HOME/.nvm}
+export NVM_DIR="${NVM_DIR:-$HOME/.nvm}"
 # This loads nvm
-if _bash_it_homebrew_check && [ -s "${BASH_IT_HOMEBREW_PREFIX}/nvm.sh" ]
+if _bash_it_homebrew_check && [[ -s "${BASH_IT_HOMEBREW_PREFIX}/nvm.sh" ]]
 then
-  . "${BASH_IT_HOMEBREW_PREFIX}/nvm.sh"
+  source "${BASH_IT_HOMEBREW_PREFIX}/nvm.sh"
 else
-  [ -s "$NVM_DIR/nvm.sh" ] && . "$NVM_DIR/nvm.sh"
+  [[ -s "$NVM_DIR/nvm.sh" ]] && source "$NVM_DIR/nvm.sh"
 fi
 
-if ! command -v nvm &>/dev/null
+if ! _command_exists nvm
 then
   function nvm() {
     echo "Bash-it no longer bundles the nvm script. Please install the latest version from"
diff --git a/plugins/available/plenv.plugin.bash b/plugins/available/plenv.plugin.bash
index 1da2d61b..79a9cf49 100644
--- a/plugins/available/plenv.plugin.bash
+++ b/plugins/available/plenv.plugin.bash
@@ -1,18 +1,16 @@
+# shellcheck shell=bash
+#
 # plugin for plenv
 
 cite about-plugin
 about-plugin 'plenv plugin for Perl'
 
-if [[ -e "${HOME}/.plenv/bin" ]] ; then
-
-  # load plenv bin dir into path if it exists
-  pathmunge "${HOME}/.plenv/bin"
-
+if [[ -d "${HOME}/.plenv/bin" ]]; then
+	# load plenv bin dir into path if it exists
+	pathmunge "${HOME}/.plenv/bin"
 fi
 
-if [[ `which plenv` ]] ; then
-
-  # init plenv
-  eval "$(plenv init - bash)"
-
+if _command_exists plenv; then
+	# init plenv
+	eval "$(plenv init - bash)"
 fi
diff --git a/plugins/available/powerline.plugin.bash b/plugins/available/powerline.plugin.bash
index 3d91e658..1927bf3e 100644
--- a/plugins/available/powerline.plugin.bash
+++ b/plugins/available/powerline.plugin.bash
@@ -1,9 +1,9 @@
-#!/usr/bin/env bash
+# shellcheck shell=bash
 
 cite about-plugin
 about-plugin 'enables powerline daemon'
 
-command -v powerline-daemon &>/dev/null || return
+_command_exists powerline-daemon || return
 powerline-daemon -q
 
 #the following should not be executed if bashit powerline themes in use
@@ -14,13 +14,13 @@ case "$BASH_IT_THEME" in
 esac
 POWERLINE_BASH_CONTINUATION=1
 POWERLINE_BASH_SELECT=1
-bashPowerlineInit=$(python -c \
+bashPowerlineInit="$(python -c \
 	"import os; \
 	import powerline;\
 	print(os.path.join(os.path.dirname(\
 	powerline.__file__),\
 	'bindings', \
 	'bash', \
-	'powerline.sh'))")
+	'powerline.sh'))")"
 [ -e $bashPowerlineInit ] || return
-. $bashPowerlineInit
+source $bashPowerlineInit
diff --git a/plugins/available/pyenv.plugin.bash b/plugins/available/pyenv.plugin.bash
index 4d8db4fb..dc8df3ad 100644
--- a/plugins/available/pyenv.plugin.bash
+++ b/plugins/available/pyenv.plugin.bash
@@ -1,12 +1,15 @@
+# shellcheck shell=bash
 cite about-plugin
 about-plugin 'load pyenv, if you are using it'
 
 export PYENV_ROOT="$HOME/.pyenv"
 pathmunge "$PYENV_ROOT/bin"
 
-[[ `which pyenv 2>/dev/null` ]] && eval "$(pyenv init - bash)"
+if _command_exists pyenv; then
+	eval "$(pyenv init - bash)"
+fi
 
 #Load pyenv virtualenv if the virtualenv plugin is installed.
 if pyenv virtualenv-init - &> /dev/null; then
-  eval "$(pyenv virtualenv-init - bash)"
+	eval "$(pyenv virtualenv-init - bash)"
 fi
diff --git a/plugins/available/rbenv.plugin.bash b/plugins/available/rbenv.plugin.bash
index 2b01669d..f3605f58 100644
--- a/plugins/available/rbenv.plugin.bash
+++ b/plugins/available/rbenv.plugin.bash
@@ -1,7 +1,10 @@
+# shellcheck shell=bash
 cite about-plugin
 about-plugin 'load rbenv, if you are using it'
 
 export RBENV_ROOT="$HOME/.rbenv"
 pathmunge "$RBENV_ROOT/bin"
 
-[[ `which rbenv 2>/dev/null` ]] && eval "$(rbenv init - bash)"
+if _command_exists rbenv; then
+	eval "$(rbenv init - bash)"
+fi
diff --git a/plugins/available/ruby.plugin.bash b/plugins/available/ruby.plugin.bash
index 4ab891d9..b1164106 100644
--- a/plugins/available/ruby.plugin.bash
+++ b/plugins/available/ruby.plugin.bash
@@ -1,9 +1,11 @@
+# shellcheck shell=bash
 cite about-plugin
 about-plugin 'ruby and rubygems specific functions and settings'
 
 # Make commands installed with 'gem install --user-install' available
 # ~/.gem/ruby/${RUBY_VERSION}/bin/
-if which ruby >/dev/null && which gem >/dev/null; then
+if _command_exists ruby && _command_exists gem
+then
   pathmunge "$(ruby -e 'print Gem.user_dir')/bin" after
 fi
 
diff --git a/plugins/available/textmate.plugin.bash b/plugins/available/textmate.plugin.bash
index e3538c1e..5c81f195 100644
--- a/plugins/available/textmate.plugin.bash
+++ b/plugins/available/textmate.plugin.bash
@@ -1,7 +1,9 @@
+# shellcheck shell=bash
 cite about-plugin
 about-plugin 'set textmate as a default editor'
 
-if $(command -v mate &> /dev/null) ; then
-  export EDITOR="$(which mate) -w"
-  export GIT_EDITOR=$EDITOR
+if _command_exists mate; then
+	EDITOR="$(type -p mate) -w"
+	GIT_EDITOR="$EDITOR"
+	export EDITOR GIT_EDITOR
 fi
diff --git a/plugins/available/virtualenv.plugin.bash b/plugins/available/virtualenv.plugin.bash
index f1c85987..41d55ddf 100644
--- a/plugins/available/virtualenv.plugin.bash
+++ b/plugins/available/virtualenv.plugin.bash
@@ -1,12 +1,14 @@
+# shellcheck shell=bash
+#
 # make sure virtualenvwrapper is enabled if available
 
 cite about-plugin
 about-plugin 'virtualenvwrapper and pyenv-virtualenvwrapper helper functions'
 
 if _command_exists pyenv; then
-  pyenv virtualenvwrapper
-else
-  [[ `which virtualenvwrapper.sh` ]] && . virtualenvwrapper.sh
+	pyenv virtualenvwrapper
+elif _command_exists virtualenvwrapper.sh; then
+	source virtualenvwrapper.sh
 fi
 
 
diff --git a/themes/base.theme.bash b/themes/base.theme.bash
index 1e0409d3..f9f5190d 100644
--- a/themes/base.theme.bash
+++ b/themes/base.theme.bash
@@ -396,7 +396,7 @@ function hg_prompt_vars {
 
 function nvm_version_prompt {
 	local node
-	if declare -f -F nvm &> /dev/null; then
+	if _is_function nvm; then
 		node=$(nvm current 2> /dev/null)
 		[[ "${node}" == "system" ]] && return
 		echo -e "${NVM_THEME_PROMPT_PREFIX}${node}${NVM_THEME_PROMPT_SUFFIX}"
@@ -433,8 +433,8 @@ function rbfu_version_prompt {
 }
 
 function chruby_version_prompt {
-	if declare -f -F chruby &> /dev/null; then
-		if declare -f -F chruby_auto &> /dev/null; then
+	if _is_function chruby; then
+		if _is_function chruby_auto; then
 			chruby_auto
 		fi
 
diff --git a/themes/dulcie/dulcie.theme.bash b/themes/dulcie/dulcie.theme.bash
old mode 100644
new mode 100755
index a83b62fb..f70c7864
--- a/themes/dulcie/dulcie.theme.bash
+++ b/themes/dulcie/dulcie.theme.bash
@@ -77,7 +77,7 @@ dulcie_prompt() {
   printf "\033]0;%s@%s:%s\007" "${USER}" "${HOSTNAME%%.*}" "${PWD/#$HOME/\~}"
 
   # Open the new terminal in the same directory
-  declare -f __vte_osc7 > /dev/null && __vte_osc7
+  _is_function __vte_osc7 && __vte_osc7
 
   PS1="${reset_color}[${DULCIE_USER}@${DULCIE_HOST}$(scm_prompt_info)${reset_color} ${DULCIE_WORKINGDIR}]"
   if [[ "${DULCIE_MULTILINE}" -eq "1" ]]; then