diff --git a/bin/chruby-exec b/bin/chruby-exec
index 4648c5c0..40d1cee7 100755
--- a/bin/chruby-exec
+++ b/bin/chruby-exec
@@ -5,7 +5,7 @@ source "$chruby_sh"
 
 case "$1" in
 	-h|--help)
-		echo "usage: chruby-exec RUBY [RUBYOPTS] -- COMMAND [ARGS...]"
+		echo "usage: chruby-exec RUBY [RUBYOPTS] [\"RUBIES=(...)\"] -- COMMAND [ARGS...]"
 		exit
 		;;
 	-V|--version)
@@ -24,7 +24,9 @@ argv=()
 for arg in "$@"; do
 	shift
 
-	if [[ "$arg" == "--" ]]; then break
+	if echo "$arg" | grep -q '^RUBIES=('; then
+		CUSTOM_RUBIES="$arg"
+	elif [[ "$arg" == "--" ]]; then break
 	else                          argv+=($arg)
 	fi
 done
@@ -38,6 +40,7 @@ shell_opts=("-l")
 [[ -t 0 ]] && shell_opts+=("-i")
 
 source_command="command -v chruby >/dev/null || source $chruby_sh"
+[[ -n "$CUSTOM_RUBIES" ]] && source_command+="; $CUSTOM_RUBIES"
 chruby_command="chruby $(printf "%q " "${argv[@]}")"
 sub_command="$(printf "%q " "$@")"
 command="$source_command; $chruby_command && $sub_command"
diff --git a/share/chruby/chruby.sh b/share/chruby/chruby.sh
index 29e6b243..5c0720d0 100644
--- a/share/chruby/chruby.sh
+++ b/share/chruby/chruby.sh
@@ -1,10 +1,53 @@
 CHRUBY_VERSION="0.3.9"
-RUBIES=()
 
-for dir in "$PREFIX/opt/rubies" "$HOME/.rubies"; do
-	[[ -d "$dir" && -n "$(ls -A "$dir")" ]] && RUBIES+=("$dir"/*)
-done
-unset dir
+function chruby_list_rubies()
+{
+	local chruby_entry
+	for chruby_entry in "$@"; do
+		[[ -x "$chruby_entry/bin/ruby" ]] && echo "$chruby_entry"
+	done 
+}
+
+function chruby_detect_rubies()
+{
+	if [[ -d "$1" ]]; then
+		{ chruby_list_rubies "$1"/* ;} 2>/dev/null || true
+	else
+		chruby_list_rubies $1
+	fi
+}
+
+function chruby_stable_version_sort() {
+	local dir ruby engine ver old_ver v0 v1 v2 v3 v4
+	sort | uniq | while read -r dir; do
+		ruby="${dir##*/}"; engine="${ruby%%-*}"; version="${ruby#*-}"
+		v0="${ver%%\.*}"; ver="${ver#*\.}"
+		v1="${ver%%\.*}"; old_ver="$ver"; ver="${ver#*\.}"
+		[[ "$ver" == "$old_ver" ]] && ver=""
+		v2="${ver%%\.*}"; old_ver="$ver"; ver="${ver#*\.}"
+		[[ "$ver" == "$old_ver" ]] && ver=""
+		v3="${ver%%\.*}"; old_ver="$ver"; ver="${ver#*\.}"
+		[[ "$ver" == "$old_ver" ]] && ver=""
+		v4="${v2#*-p}"
+		[[ "$v2" == "$v4" ]] && v4=""
+		echo "$engine:$v0:$v1:$v2:$v3:$v4:$dir"
+	done | sort -n -t: -k1,1 -k2,2 -k3,3 -k4,4 -k5,5 -k6,6 | cut -d: -f7-
+}
+
+function chruby_detect_all_rubies()
+{
+	{
+		chruby_detect_rubies "$PREFIX/opt/rubies"
+		chruby_detect_rubies "$HOME/.rubies"
+		if [[ -n "$RUBIES" ]]; then
+			local chruby_rubies_dir
+			for chruby_rubies_dir in "${RUBIES[@]}"; do
+				chruby_detect_rubies "$chruby_rubies_dir"
+			done
+		fi
+	} | chruby_stable_version_sort
+}
+
 
 function chruby_reset()
 {
@@ -30,6 +73,22 @@ function chruby_reset()
 	hash -r
 }
 
+function chruby_generate_cached_env()
+{
+	"$SHELL" -c "unset JAVACMD JRUBY_OPTS; RUBYGEMS_GEMDEPS='' '$RUBY_ROOT/bin/ruby' -" <<'SCRIPT'
+env = {
+  :RUBY_ENGINE  => Object.const_defined?(:RUBY_ENGINE) ? RUBY_ENGINE : 'ruby',
+  :RUBY_VERSION => RUBY_VERSION,
+}
+begin
+  require 'rubygems'
+  env[:GEM_ROOT] = Gem.default_dir
+rescue LoadError
+end
+env.each { |k,v| puts "#{k}='#{v}'; export #{k}" }
+SCRIPT
+}
+
 function chruby_use()
 {
 	if [[ ! -x "$1/bin/ruby" ]]; then
@@ -42,13 +101,12 @@ function chruby_use()
 	export RUBY_ROOT="$1"
 	export RUBYOPT="$2"
 	export PATH="$RUBY_ROOT/bin:$PATH"
+	local ruby_cached_env="$RUBY_ROOT/.ruby_env"
+	if [[ ! -e "$ruby_cached_env" ]]; then
+		chruby_generate_cached_env > "$ruby_cached_env"
+	fi
+	. "$ruby_cached_env"
 
-	eval "$(RUBYGEMS_GEMDEPS="" "$RUBY_ROOT/bin/ruby" - <<EOF
-puts "export RUBY_ENGINE=#{Object.const_defined?(:RUBY_ENGINE) ? RUBY_ENGINE : 'ruby'};"
-puts "export RUBY_VERSION=#{RUBY_VERSION};"
-begin; require 'rubygems'; puts "export GEM_ROOT=#{Gem.default_dir.inspect};"; rescue LoadError; end
-EOF
-)"
 	export PATH="${GEM_ROOT:+$GEM_ROOT/bin:}$PATH"
 
 	if (( UID != 0 )); then
@@ -71,7 +129,7 @@ function chruby()
 			;;
 		"")
 			local dir ruby
-			for dir in "${RUBIES[@]}"; do
+			chruby_detect_all_rubies | while read -r dir; do
 				dir="${dir%%/}"; ruby="${dir##*/}"
 				if [[ "$dir" == "$RUBY_ROOT" ]]; then
 					echo " * ${ruby} ${RUBYOPT}"
@@ -84,7 +142,7 @@ function chruby()
 		system) chruby_reset ;;
 		*)
 			local dir ruby match
-			for dir in "${RUBIES[@]}"; do
+			chruby_detect_all_rubies | while read -r dir; do
 				dir="${dir%%/}"; ruby="${dir##*/}"
 				case "$ruby" in
 					"$1")	match="$dir" && break ;;