diff --git a/samples/part1/bin/ruby-ls b/samples/part1/bin/ruby-ls
index f10c79a..c90f1e4 100755
--- a/samples/part1/bin/ruby-ls
+++ b/samples/part1/bin/ruby-ls
@@ -1,4 +1,26 @@
 #!/usr/bin/env ruby
 
-## FIXME: Replace this code with a pure Ruby clone of the ls utility
-system("ls", *ARGV)
+require 'optparse'
+
+require_relative '../lib/ruby_ls'
+
+options = {}
+parser = OptionParser.new do |p|
+  p.on('-l') { options[:long_format]    = true }
+  p.on('-a') { options[:include_hidden] = true }
+end
+
+begin
+  paths = parser.parse(ARGV)
+rescue OptionParser::InvalidOption => err
+  msg = err.message.sub('invalid', 'illegal').sub(': -', ' -- ')
+  usage = 'usage: ls [-ABCFGHLOPRSTUWabcdefghiklmnopqrstuwx1] [file ...]'
+  abort "ls: #{msg}\n#{usage}"
+end
+paths << Dir.pwd if paths.empty?
+
+begin
+  RubyLS::Application.new(options, paths).run
+rescue Errno::ENOENT => err
+  abort "ls: #{err.message}"
+end
diff --git a/samples/part1/lib/ruby_ls.rb b/samples/part1/lib/ruby_ls.rb
new file mode 100644
index 0000000..71211d7
--- /dev/null
+++ b/samples/part1/lib/ruby_ls.rb
@@ -0,0 +1,4 @@
+require_relative 'ruby_ls/application'
+require_relative 'ruby_ls/display'
+require_relative 'ruby_ls/file_details'
+require_relative 'ruby_ls/permissions'
diff --git a/samples/part1/lib/ruby_ls/application.rb b/samples/part1/lib/ruby_ls/application.rb
new file mode 100644
index 0000000..2b6b413
--- /dev/null
+++ b/samples/part1/lib/ruby_ls/application.rb
@@ -0,0 +1,43 @@
+module RubyLS
+  class Application
+    def initialize(options, paths)
+      @options = options
+      @paths   = paths
+      @display = RubyLS::Display.new(display_options)
+    end
+
+    def run
+      @paths.each { |p| @display.render(p) }
+    end
+
+    private
+
+    def display_options
+      @options.merge(max_byte_count: byte_counts.max)
+    end
+
+    def byte_counts
+      @paths.flat_map do |p|
+        Dir.exist?(p) ? directory_byte_counts(p) : byte_count(p)
+      end
+    end
+
+    def directory_byte_counts(path)
+      directory_subpaths(path).map { |p| byte_count(p) }
+    end
+
+    def directory_subpaths(path)
+      non_dot_char = /[^\.]/
+
+      Dir.foreach(path)
+         .select { |e| e =~ non_dot_char }
+         .map    { |e| File.join(path, e) }
+    end
+
+    def byte_count(path)
+      File.stat(path).size
+    rescue Errno::ENOENT => e
+      raise(e, "#{path}: No such file or directory")
+    end
+  end
+end
diff --git a/samples/part1/lib/ruby_ls/display.rb b/samples/part1/lib/ruby_ls/display.rb
new file mode 100644
index 0000000..1b8d960
--- /dev/null
+++ b/samples/part1/lib/ruby_ls/display.rb
@@ -0,0 +1,65 @@
+module RubyLS
+  class Display
+    def initialize(options)
+      @long_format    = options[:long_format]
+      @include_hidden = options[:include_hidden]
+      @max_byte_count = options[:max_byte_count]
+    end
+
+    def render(path)
+      if Dir.exist?(path)
+        render_directory(path)
+      else
+        render_file(path)
+      end
+    end
+
+    private
+
+    def render_directory(dirname)
+      list_total_blocks(dirname) if @long_format
+      Dir.foreach(dirname) { |e| render_file(e) }
+    end
+
+    def list_total_blocks(dirname)
+      puts "total #{total_blocks(dirname)}"
+    end
+
+    def total_blocks(dirname)
+      entries(dirname).reduce(0) do |sum, e|
+        path = File.join(dirname, e)
+        sum + blocks_allocated(path)
+      end
+    end
+
+    def entries(dirname)
+      Dir.entries(dirname).select { |e| show?(e) }
+    end
+
+    def blocks_allocated(path)
+      File.stat(path).blocks
+    end
+
+    def render_file(filename)
+      if show?(filename)
+        puts formatted(filename)
+      end
+    end
+
+    def show?(filename)
+      @include_hidden || !hidden?(filename)
+    end
+
+    def hidden?(filename)
+      filename[0] == '.'
+    end
+
+    def formatted(filename)
+      if @long_format
+        File.open(filename) { |f| RubyLS::FileDetails.new(f, @max_byte_count) }
+      else
+        filename
+      end
+    end
+  end
+end
diff --git a/samples/part1/lib/ruby_ls/file_details.rb b/samples/part1/lib/ruby_ls/file_details.rb
new file mode 100644
index 0000000..7776dc1
--- /dev/null
+++ b/samples/part1/lib/ruby_ls/file_details.rb
@@ -0,0 +1,69 @@
+require 'etc'
+
+module RubyLS
+  class FileDetails
+    FTYPES = {
+      'blockSpecial'     => 'b',
+      'characterSpecial' => 'c',
+      'directory'        => 'd',
+      'link'             => 'l',
+      'socket'           => 's',
+      'fifo'             => 'P',
+      'file'             => '-'
+    }
+
+    def initialize(file, max_byte_count = nil)
+      @file = file
+      @stat = File.stat(@file)
+      @permissions = RubyLS::Permissions.new(@stat)
+      @max_byte_count = max_byte_count
+    end
+
+    def to_s
+      "#{mode} #{links.to_s.rjust(2)} #{owner}  #{group} #{bytes} #{mtime} #{path}"
+    end
+
+    def [](key)
+      send(key)
+    end
+
+    private
+
+    attr_reader :permissions
+
+    def mode
+      ftype = FTYPES[@stat.ftype]
+      "#{ftype}#{permissions}"
+    end
+
+    def links
+      @stat.nlink
+    end
+
+    def owner
+      Etc.getpwuid(@stat.uid).name
+    end
+
+    def group
+      Etc.getgrgid(@stat.gid).name
+    end
+
+    def bytes
+      col_width = (@max_byte_count || size).to_s.length + 1
+      size.to_s.rjust(col_width)
+    end
+
+    def size
+      @stat.size
+    end
+
+    def mtime
+      time = @stat.mtime
+      time.strftime('%b %e %H:%M')
+    end
+
+    def path
+      @file.path
+    end
+  end
+end
diff --git a/samples/part1/lib/ruby_ls/permissions.rb b/samples/part1/lib/ruby_ls/permissions.rb
new file mode 100644
index 0000000..099dc12
--- /dev/null
+++ b/samples/part1/lib/ruby_ls/permissions.rb
@@ -0,0 +1,36 @@
+module RubyLS
+  class Permissions
+    ACTORS = [:owner, :group, :other]
+    OPERATIONS = [:r, :w, :x]
+
+    def initialize(file_stat)
+      @fmode = file_stat.mode
+    end
+
+    def to_s
+      symbols.join
+    end
+
+    private
+
+    def symbols
+      bit_masks.map do |mask, operation|
+        enabled?(@fmode & mask) ? operation : :-
+      end
+    end
+
+    def bit_masks
+      msb_masks = lsb_masks.reverse
+      msb_masks.zip(OPERATIONS.cycle)
+    end
+
+    def lsb_masks
+      bits = (ACTORS.count * OPERATIONS.count)
+      bits.times.map { |offset| 0b1 << offset }
+    end
+
+    def enabled?(bits)
+      bits > 0
+    end
+  end
+end
diff --git a/samples/part1/ls_tests.rb b/samples/part1/ls_tests.rb
index 4371b25..04f0979 100644
--- a/samples/part1/ls_tests.rb
+++ b/samples/part1/ls_tests.rb
@@ -7,21 +7,21 @@
 
 # TODO: Uncomment each test below and get it to pass.
 
-# check("Dir listing", "foo")
+check("Dir listing", "foo")
 
-# check("File glob", "foo/*.txt")
+check("File glob", "foo/*.txt")
 
-# check("Detailed output", "-l")
+check("Detailed output", "-l")
 
-# check("Hidden files", "-a")
+check("Hidden files", "-a")
 
-# check("Hidden files with detailed output", "-a -l")
+check("Hidden files with detailed output", "-a -l")
 
-# check("File glob with detailed output", "-l foo/*.txt")
+check("File glob with detailed output", "-l foo/*.txt")
 
-# check("Invalid directory", "missingdir")
+check("Invalid directory", "missingdir")
 
-# check("Invalid flag", "-Z")
+check("Invalid flag", "-Z")
 
 puts "You passed the tests, yay!"