diff --git a/.gitignore b/.gitignore
index 9106b2a..ff7246f 100644
--- a/.gitignore
+++ b/.gitignore
@@ -6,3 +6,4 @@
 /pkg/
 /spec/reports/
 /tmp/
+*.sw[o-t]
diff --git a/lib/dencli.rb b/lib/dencli.rb
index 745bdbb..0c09257 100755
--- a/lib/dencli.rb
+++ b/lib/dencli.rb
@@ -4,6 +4,11 @@ class DenCli
 	class UnknownCommand < UsageError
 	end
 
+	require_relative 'dencli/cmd'
+	require_relative 'dencli/sub'
+	require_relative 'dencli/interactive'
+	require_relative 'dencli/version'
+
 	class <<self
 		# Helper Function for generate Regular Expressions of string,
 		# which matches all strings which has parts fron beginning of the given string.
@@ -47,107 +52,7 @@ class DenCli
 		alias g gen_aliases
 	end
 
-	class CMD
-		attr_reader :parent, :name, :desc, :exe
-		def initialize parent, name, desc, exe
-			raise "Proc expected, instead of: #{exe.inspect}"  unless Proc === exe
-			@parent, @name, @desc, @exe = parent, name, desc, exe
-		end
-
-		def _full_cmd post
-			parent._full_cmd [@name]+post
-		end
-
-		def full_cmd
-			_full_cmd []
-		end
-
-		def call *a
-			@exe.call *a
-		end
-
-		def help
-			"#{parent.full_cmd.join ' '} #{name}\n#{    desc}"
-		end
-
-		def inspect
-			"#<%s:0x%x %s @name=%p @desc=%p @parent=<%s:0x%x %s> @exe=<arity=%d>>" % [
-				self.class.name, self.object_id, self.full_cmd,
-				@name, @desc, @parent.class.name, @parent.class.object_id, @parent.full_cmd,
-				@exe.arity
-			]
-		end
-	end
-
-	class Sub
-		attr_reader :parent, :name, :desc, :subs
-		def initialize parent, name, desc
-			@parent, @name, @desc, @subs, @aliases = parent, name, desc, {}, {}
-		end
-
-		def _full_cmd post
-			parent._full_cmd [@name]+post
-		end
-
-		def full_cmd
-			_full_cmd []
-		end
-
-		def [] k
-			@aliases[k]
-		end
-
-		def help n = nil, *a
-			if n.nil?
-				r = "#{full_cmd.join ' '}: #{desc}\n\n"
-				m = @subs.map {|k,_| k.length }.max
-				@subs.each do |k, c|
-					r += "  % -#{m}s  %s\n" % [k, c.desc]  unless k.nil?
-				end
-				r
-			elsif @aliases.has_key? n
-				@aliases[n].help *a
-			else
-				raise UnknownCommand, "unknown command: #{_full_cmd( [n])[1..-1].join ' '}, available for #{full_cmd[1..-1].join' '}: #{@subs.keys.inspect}"
-			end
-		end
-
-		def call *a
-			n, *a = *a
-			if @aliases.has_key? n
-				@aliases[n].call *a
-			else
-				raise UnknownCommand, "unknown command: #{_full_cmd( [n])[1..-1].join ' '}, available for #{full_cmd[1..-1].join' '}: #{@subs.keys.inspect}"
-			end
-		end
-
-		def _add name, min, obj, aliases
-			name = name.to_s  unless name.nil?
-			@subs[name] = obj
-			DenCli.gen_aliases( name, min) {|a| @aliases[a] = obj }
-			if aliases
-				[*aliases].each {|a| @aliases[a] = obj }
-			end
-			obj
-		end
-		private :_add
-
-		def sub name, desc, min: nil, aliases: nil, &exe
-			r = _add name, min, Sub.new( self, name, desc), aliases
-			block_given? ? yield( r) : r
-		end
-
-		def cmd name, desc, min: nil, aliases: nil, &exe
-			_add name, min, CMD.new( self, name, desc, exe), aliases
-		end
-
-		def inspect
-			"#<%s:0x%x %s @name=%p @desc=%p @subs={%s} @aliases={%s} @parent=<%s:0x%x %s>>" % [
-				self.class.name, self.object_id, self.full_cmd,
-				@name, @desc, @subs.keys.join(', '), @aliases.keys.join(', '), @parent.class.name, @parent.class.object_id, @parent.full_cmd
-			]
-		end
-	end
+	attr_reader :subs
 
 	def initialize progname, desc
 		@subs = Sub.new self, progname, desc
@@ -180,4 +85,8 @@ class DenCli
 	def [] k
 		@subs[k]
 	end
+
+	def interactive *args, **opts
+		Interactive.new self, *args, **opts
+	end
 end
diff --git a/lib/dencli/cmd.rb b/lib/dencli/cmd.rb
new file mode 100644
index 0000000..0633bfb
--- /dev/null
+++ b/lib/dencli/cmd.rb
@@ -0,0 +1,31 @@
+require_relative '../dencli'
+
+class DenCli::CMD
+	attr_reader :parent, :name, :desc, :exe, :completion
+
+	def initialize parent, name, desc, exe
+		raise "Proc expected, instead of: #{exe.inspect}"  unless Proc === exe
+		@parent, @name, @desc, @exe = parent, name, desc, exe
+		completion {|*a| [] }
+	end
+
+	def _full_cmd( post) parent._full_cmd [@name]+post end
+	def full_cmd() _full_cmd [] end
+	def call( *a) @exe.call *a end
+	def help() "#{parent.full_cmd.join ' '} #{name}\n#{    desc}" end
+
+	def complete( *pre, str) @completion.call *pre, str end
+
+	def completion &exe
+		@completion = exe
+		self
+	end
+
+	def inspect
+		"#<%s:0x%x %s @name=%p @desc=%p @parent=<%s:0x%x %s> @exe=<arity=%d>>" % [
+			self.class.name, self.object_id, self.full_cmd,
+			@name, @desc, @parent.class.name, @parent.class.object_id, @parent.full_cmd,
+			@exe.arity
+		]
+	end
+end
diff --git a/lib/dencli/interactive.rb b/lib/dencli/interactive.rb
new file mode 100644
index 0000000..69eb07e
--- /dev/null
+++ b/lib/dencli/interactive.rb
@@ -0,0 +1,133 @@
+require_relative '../dencli'
+
+class DenCli::Interactive
+	attr_reader :cl, :prompt, :cur, :histfile
+
+	def initialize cl, prompt, histfile: nil
+		require 'readline'
+		@cl, self.prompt = cl, prompt
+		@cur = cl.subs
+		cur.instance_variable_set :@name, ''
+
+		@histfile =
+			case histfile
+			when nil then nil
+			when Pathname then histfile
+			else Pathname.new histfile.to_s
+			end
+		read_history  if @histfile
+
+		Readline.vi_editing_mode  rescue NotImplementedError
+		Readline.completion_append_character = " "
+		Readline.completion_proc = method :complete
+
+		prepare_sub cl.subs
+		cl.cmd :exit, "exit", min: 2 do
+			exit 0
+		end
+		cl.subs.aliases['?'] = cl.subs.subs['help']
+		cl.subs.subs.delete 'cli'
+
+		stty_save = %x`stty -g`.chomp
+		trap "INT" do
+			system "stty", stty_save
+			Readline.refresh_line
+		end
+	end
+
+	def history_file file = nil
+		file =
+			case file
+			when Pathname then file
+			when nil then @histfile
+			else Pathname.new file.to_s
+			end
+	end
+
+	def read_history file = nil
+		file = history_file file
+		return  unless file and file.exist?
+		file.each_line do |line|
+			Readline::HISTORY.push line.chomp
+		end
+	end
+
+	def write_history file = nil
+		file = history_file file
+		return  unless file
+		file.open 'w+' do |f|
+			Readline::HISTORY.each do |line|
+				f.puts line
+			end
+		end
+	end
+
+	def prompt= s
+		@prompt = s.to_s
+	end
+
+	def complete s
+		ws = words Readline.line_buffer
+		@cur.complete *ws[0...-1], s
+	end
+
+	def sub *args, cur: nil
+		args.inject( cur || @cur) do |r, a|
+			return nil  unless r.is_a? DenCli::Sub
+			r[a]
+		end
+	end
+	private :sub
+
+	def words line = nil
+		r = line.split " "
+		r.push ''  if ' ' == line[-1]
+		r
+	end
+	private :words
+
+	def prepare_sub c
+		c.subs.values.each do |n|
+			case n
+			when DenCli::Sub
+				n.cmd :exit, "<- #{n.parent.full_cmd.join ' '} - #{n.parent.desc[3..-1]}", min: 2 do
+					@cur = n.parent
+				end
+				n.cmd '', "", min: 2, aliases: [nil] do
+					@cur = n
+				end
+				n.subs.delete ''
+				n.aliases['?'] = n.subs['help']
+				prepare_sub n
+			when DenCli::CMD
+			else raise "Unsupported sub-type: #{x}"
+			end
+		end
+	end
+
+	def read
+		line = Readline.readline( "#{prompt}#{cur.full_cmd.join ' '}> ", true)
+		return nil  if line.nil?
+		Readline::HISTORY.pop  if /^\s*$/ =~ line
+		if 0 < Readline::HISTORY.length-2 and Readline::HISTORY[Readline::HISTORY.length-2] == line
+			Readline::HISTORY.pop
+		end
+		line.split " "
+	end
+
+	def step
+		line = read
+		return nil  if line.nil?
+		begin
+			cur.call *line
+		rescue ::UsageError
+			STDERR.puts "! #$!"
+		end
+		true
+	end
+
+	def run
+		while step
+		end
+	end
+end
diff --git a/lib/dencli/sub.rb b/lib/dencli/sub.rb
new file mode 100644
index 0000000..e822e1d
--- /dev/null
+++ b/lib/dencli/sub.rb
@@ -0,0 +1,74 @@
+require_relative '../dencli'
+
+class DenCli::Sub
+	attr_reader :parent, :name, :desc, :subs, :aliases
+
+	def initialize parent, name, desc
+		@parent, @name, @desc, @subs, @aliases = parent, name, "-> #{desc}", {}, {}
+	end
+
+	def _full_cmd( post) parent._full_cmd [@name]+post end
+	def full_cmd() _full_cmd [] end
+	def []( k) @aliases[k] end
+
+	def help n = nil, *a
+		if n.nil?
+			r = "#{full_cmd.join ' '}: #{desc}\n\n"
+			m = @subs.map {|k,_| k.length }.max
+			@subs.each do |k, c|
+				r += "  % -#{m}s  %s\n" % [k, c.desc]  unless k.nil?
+			end
+			r
+		elsif @aliases.has_key? n
+			@aliases[n].help *a
+		else
+			raise UnknownCommand, "unknown command: #{_full_cmd( [n])[1..-1].join ' '}, available for #{full_cmd[1..-1].join' '}: #{@subs.keys.join ' '}"
+		end
+	end
+
+	def call *a
+		n, *a = *a
+		if @aliases.has_key? n
+			@aliases[n].call *a
+		else
+			raise UnknownCommand, "unknown command: #{_full_cmd( [n])[1..-1].join ' '}, available for #{full_cmd[1..-1].join' '}: #{@subs.keys.join ' '}"
+		end
+	end
+
+	def _add name, min, obj, aliases
+		name = name.to_s  unless name.nil?
+		@subs[name] = obj
+		DenCli.gen_aliases( name, min) {|a| @aliases[a] = obj }
+		if aliases
+			[*aliases].each {|a| @aliases[a] = obj }
+		end
+		obj
+	end
+	private :_add
+
+	def sub name, desc, min: nil, aliases: nil, &exe
+		r = _add name, min, DenCli::Sub.new( self, name, desc), aliases
+		block_given? ? yield( r) : r
+	end
+
+	def cmd name, desc, min: nil, aliases: nil, &exe
+		_add name, min, DenCli::CMD.new( self, name, desc, exe), aliases
+	end
+
+	def complete *pre, str
+		if pre.empty?
+			@subs.keys.grep /\A#{Regexp.escape str}/
+		elsif sub = @subs[pre[0]]
+			sub.complete *pre[1..-1], str
+		else
+			STDOUT.print "\a"
+		end
+	end
+
+	def inspect
+		"#<%s:0x%x %s @name=%p @desc=%p @subs={%s} @aliases={%s} @parent=<%s:0x%x %s>>" % [
+			self.class.name, self.object_id, self.full_cmd,
+			@name, @desc, @subs.keys.join(', '), @aliases.keys.join(', '), @parent.class.name, @parent.class.object_id, @parent.full_cmd
+		]
+	end
+end
diff --git a/lib/dencli/version.rb b/lib/dencli/version.rb
index 3ee143f..a95042a 100644
--- a/lib/dencli/version.rb
+++ b/lib/dencli/version.rb
@@ -1,3 +1,3 @@
 class DenCli
-	VERSION = '0.1.0'
+	VERSION = '0.2.0'
 end