diff --git a/ruby/a1 b/ruby/a1
index df2851c..55b8a20 100755
--- a/ruby/a1
+++ b/ruby/a1
@@ -1,3 +1,9 @@
-#!/bin/sh
+#!/usr/bin/env ruby -w
 
-./main.rb "$@"
+require 'English'
+
+$LOAD_PATH << File.expand_path(__dir__)
+
+require 'shell'
+
+Shell::CLI.new.run(args: ARGV) if $PROGRAM_NAME == __FILE__
diff --git a/ruby/main.rb b/ruby/main.rb
deleted file mode 100755
index 3134380..0000000
--- a/ruby/main.rb
+++ /dev/null
@@ -1,108 +0,0 @@
-#!/usr/bin/env ruby -w
-
-require 'English'
-require 'readline'
-require 'wordexp'
-
-require './builtins'
-require './colours'
-require './job_control'
-require './logger'
-
-# TODO: change to module after extracting all or most of the code
-class Shell
-  include Colours
-
-  attr_reader :builtins, :job_control, :logger, :options
-
-  def initialize(args: ARGV, builtins: nil, job_control: nil, logger: nil)
-    logger ||= Logger.instance
-    job_control ||= JobControl.new
-    builtins ||= Builtins.new(job_control)
-    @builtins = builtins
-    @job_control = job_control
-    @logger = logger
-    @options = parse_options(args)
-    logger.verbose "Options: #{options.inspect}"
-  end
-
-  def main
-    if options[:command]
-      logger.verbose "Executing command: #{options[:command]}"
-      print_logs
-      exit process_command(options[:command])
-    end
-    repl if $stdin.isatty
-  end
-
-  def repl
-    @job_control.trap_sigchld
-    add_to_history = true
-    status = 0
-    loop do
-      print_logs
-      print "#{red(status)} " unless status.zero?
-      line = Readline.readline(prompt(Dir.pwd), add_to_history)
-      Readline::HISTORY.pop if line.nil? || line.strip.empty?
-      status = process_command(line)
-    end
-  end
-
-  # Looks like this: /path/to/somewhere%
-  def prompt(pwd)
-    "#{blue(pwd)}#{white('%')} #{CLEAR}"
-  end
-
-  def parse_options(args)
-    options = {
-      verbose: false,
-    }
-    while (arg = args.shift)
-      case arg
-      when '-c'
-        options[:command] = args.shift
-      when '-v', '--verbose'
-        options[:verbose] = true
-      else
-        logger.warn "#{red('[ERROR]')} Unknown argument: #{arg}"
-        exit 1
-      end
-    end
-    options
-  end
-
-  def print_logs
-    logger.logs.each do |log|
-      message = "#{log.message}#{CLEAR}"
-      case log.level
-      when :verbose
-        warn message if options[:verbose]
-      else
-        warn message
-      end
-    end
-    logger.clear
-  end
-
-  def process_command(line)
-    exit 0 if line.nil? # EOF, ctrl-d
-    return 0 if line.strip.empty? # no input, no-op
-
-    logger.verbose "Processing command: #{line.inspect}"
-    args = Wordexp.expand(line)
-    cmd = args.shift
-    logger.verbose "Parsed command: #{cmd} #{args.inspect}"
-    if @builtins.builtin?(cmd)
-      logger.verbose "Executing builtin #{cmd}"
-      @builtins.exec(cmd, args)
-    else
-      logger.verbose "Shelling out for #{cmd}"
-      @job_control.exec_command(cmd, args)
-    end
-  rescue Errno => e
-    warn "#{red('[ERROR]')} #{e.message}"
-    -1
-  end
-end
-
-Shell.new(args: ARGV).main if $PROGRAM_NAME == __FILE__
diff --git a/ruby/shell.rb b/ruby/shell.rb
new file mode 100644
index 0000000..22df219
--- /dev/null
+++ b/ruby/shell.rb
@@ -0,0 +1,5 @@
+require 'shell/cli'
+require 'shell/repl'
+
+module Shell
+end
diff --git a/ruby/builtins.rb b/ruby/shell/builtins.rb
similarity index 72%
rename from ruby/builtins.rb
rename to ruby/shell/builtins.rb
index 03bb2de..98ebad4 100644
--- a/ruby/builtins.rb
+++ b/ruby/shell/builtins.rb
@@ -1,9 +1,13 @@
-class Shell
-  class Builtins
-    attr_reader :logger
+require 'shell/job_control'
+require 'shell/logger'
 
-    def initialize(job_control, logger = Logger.instance)
-      @job_control = job_control
+module Shell
+  class Builtins
+    attr_reader :job_control, :logger
+
+    def initialize(job_control: nil, logger: nil)
+      logger ||= Logger.instance
+      @job_control = job_control || JobControl.new(logger: logger)
       @logger = logger
     end
 
@@ -21,7 +25,7 @@ class Shell
 
     def builtin_bg(args)
       cmd = args.shift
-      @job_control.exec_command(cmd, args, background: true)
+      job_control.exec_command(cmd, args, background: true)
     end
 
     def builtin_cd(args)
diff --git a/ruby/shell/cli.rb b/ruby/shell/cli.rb
new file mode 100644
index 0000000..1cf74bd
--- /dev/null
+++ b/ruby/shell/cli.rb
@@ -0,0 +1,61 @@
+require 'shell/colours'
+require 'shell/logger'
+require 'shell/repl'
+
+module Shell
+  class CLI
+    include Colours
+
+    attr_reader :logger, :options, :repl
+
+    def initialize(logger: nil, repl: nil)
+      @logger = logger || Logger.instance
+      @options = {}
+      @repl = repl || REPL.new(logger: @logger)
+      @repl.precmd_hook = -> { print_logs }
+    end
+
+    def run(args: nil)
+      @options = parse_options(args || ARGV)
+      logger.verbose "Options: #{options.inspect}"
+      if options[:command]
+        logger.verbose "Executing command: #{options[:command]}"
+        print_logs
+        exit repl.process_command(options[:command])
+      elsif $stdin.isatty
+        repl.start(options: options)
+      end
+    end
+
+    def parse_options(args)
+      options = {
+        verbose: false,
+      }
+      while (arg = args.shift)
+        case arg
+        when '-c'
+          options[:command] = args.shift
+        when '-v', '--verbose'
+          options[:verbose] = true
+        else
+          logger.warn "#{red('[ERROR]')} Unknown argument: #{arg}"
+          exit 1
+        end
+      end
+      options
+    end
+
+    def print_logs
+      logger.logs.each do |log|
+        message = "#{log.message}#{CLEAR}"
+        case log.level
+        when :verbose
+          warn message if options[:verbose]
+        else
+          warn message
+        end
+      end
+      logger.clear
+    end
+  end
+end
diff --git a/ruby/colours.rb b/ruby/shell/colours.rb
similarity index 97%
rename from ruby/colours.rb
rename to ruby/shell/colours.rb
index 9489e68..f2b809a 100644
--- a/ruby/colours.rb
+++ b/ruby/shell/colours.rb
@@ -1,4 +1,4 @@
-class Shell
+module Shell
   module Colours
     # These colours should be safe on dark and light backgrounds.
     BLUE = "\033[1;34m".freeze
diff --git a/ruby/job.rb b/ruby/shell/job.rb
similarity index 78%
rename from ruby/job.rb
rename to ruby/shell/job.rb
index ff546a0..f3f4eeb 100644
--- a/ruby/job.rb
+++ b/ruby/shell/job.rb
@@ -1,3 +1,3 @@
-class Shell
+module Shell
   Job = Struct.new(:id, :pid, :cmd, :args)
 end
diff --git a/ruby/job_control.rb b/ruby/shell/job_control.rb
similarity index 93%
rename from ruby/job_control.rb
rename to ruby/shell/job_control.rb
index fcb1e15..2bc42e8 100644
--- a/ruby/job_control.rb
+++ b/ruby/shell/job_control.rb
@@ -1,15 +1,18 @@
-require './colours'
-require './job'
+require 'English'
 
-class Shell
+require 'shell/colours'
+require 'shell/job'
+require 'shell/logger'
+
+module Shell
   class JobControl
     include Colours
 
     attr_reader :logger
 
-    def initialize(logger = Logger.instance)
+    def initialize(logger: nil)
       @jobs_by_pid = {}
-      @logger = logger
+      @logger = logger || Logger.instance
     end
 
     def trap_sigchld
diff --git a/ruby/logger.rb b/ruby/shell/logger.rb
similarity index 95%
rename from ruby/logger.rb
rename to ruby/shell/logger.rb
index 54720d0..a5b4954 100644
--- a/ruby/logger.rb
+++ b/ruby/shell/logger.rb
@@ -1,6 +1,6 @@
-require './colours'
+require 'shell/colours'
 
-class Shell
+module Shell
   # Queues up messages to be printed out when readline is waiting for input, to prevent
   # mixing shell output with command output.
   class Logger
diff --git a/ruby/shell/repl.rb b/ruby/shell/repl.rb
new file mode 100644
index 0000000..1a46776
--- /dev/null
+++ b/ruby/shell/repl.rb
@@ -0,0 +1,67 @@
+require 'readline'
+require 'wordexp'
+
+require 'shell/builtins'
+require 'shell/colours'
+require 'shell/job_control'
+require 'shell/logger'
+
+module Shell
+  class REPL
+    include Colours
+
+    attr_reader :builtins, :job_control, :logger, :options
+
+    attr_accessor :precmd_hook
+
+    def initialize(builtins: nil, job_control: nil, logger: nil)
+      logger ||= Logger.instance
+      job_control ||= JobControl.new(logger: logger)
+      builtins ||= Builtins.new(job_control: job_control)
+
+      @builtins = builtins
+      @job_control = job_control
+      @logger = logger
+      @options = {}
+    end
+
+    def start(options: nil)
+      @options = options || {}
+      job_control.trap_sigchld
+      add_to_history = true
+      status = 0
+      loop do
+        precmd_hook&.call
+        print "#{red(status)} " unless status.zero?
+        line = Readline.readline(prompt(Dir.pwd), add_to_history)
+        Readline::HISTORY.pop if line.nil? || line.strip.empty?
+        status = process_command(line)
+      end
+    end
+
+    def process_command(line)
+      exit 0 if line.nil? # EOF, ctrl-d
+      return 0 if line.strip.empty? # no input, no-op
+
+      logger.verbose "Processing command: #{line.inspect}"
+      args = Wordexp.expand(line)
+      cmd = args.shift
+      logger.verbose "Parsed command: #{cmd} #{args.inspect}"
+      if builtins.builtin?(cmd)
+        logger.verbose "Executing builtin #{cmd}"
+        builtins.exec(cmd, args)
+      else
+        logger.verbose "Shelling out for #{cmd}"
+        job_control.exec_command(cmd, args)
+      end
+    rescue Errno => e
+      warn "#{red('[ERROR]')} #{e.message}"
+      -1
+    end
+
+    # Looks like this: /path/to/somewhere%
+    def prompt(pwd)
+      "#{blue(pwd)}#{white('%')} #{CLEAR}"
+    end
+  end
+end