install_homebrew.rb

#!/usr/bin/ruby
#
# I deliberately didn't DRY /usr/local references into a variable as this
# script will not "just work" if you change the destination directory. However
# please feel free to fork it and make that possible.
#
# If you do fork ensure you add a comment here that explains what the changes
# are intended to do and how well you tested them.
#

module Tty extend self
  def blue; bold 34; end
  def white; bold 39; end
  def red; underline 31; end
  def reset; escape 0; end
  def underline; underline 39; end
  def bold n; escape "1;#{n}" end
  def underline n; escape "4;#{n}" end
  def escape n; "\033[#{n}m" if $stdout.tty? end
end

def ohai s
  puts "#{Tty.blue}==>#{Tty.white} #{s}#{Tty.reset}"
end

def sudo *params
  params.unshift "sudo"
  ohai params.map{ |p| p.gsub ' ', '\\ ' } * ' '
  system *params
end

def opoo warning
  puts "#{Tty.red}Warning#{Tty.reset}: #{warning}"
end

####################################################################### script
require 'fileutils'
include  FileUtils

#abort "/usr/local/.git already exists!" if File.directory? '/usr/local/.git'

ohai "This script will install:"
puts "/usr/local/bin/brew"
puts "/usr/local/Library/Formula/..."
puts "/usr/local/Library/Homebrew/..."

chmods = %w(bin etc include lib sbin share var . share/locale share/man share/info share/doc share/aclocal).
            map{ |d| "/usr/local/#{d}" }.
            select{ |d| File.directory? d and not File.writable? d }

unless chmods.empty?
  ohai "The following directories will be made group writable:"
  puts *chmods
end

puts
puts "Press enter to continue"
abort if gets != "\n"

if File.directory? '/usr/local'
  sudo "/bin/chmod", "g+w", *chmods unless chmods.empty?
else
  sudo "/bin/mkdir", '/usr/local'
  sudo "/bin/chmod", "g+w", '/usr/local'
end

cd '/usr/local' do
  tarball = "http://github.com/mxcl/homebrew/tarball/master"
  ohai "Extracting: #{tarball}"
  # -m to stop tar erroring out if it can't modify the mtime for root owned directories
  system "/usr/bin/curl -#L #{tarball} | /usr/bin/tar xz -m --strip 1"
end

ohai "Installation successful"

if ENV['PATH'].split(':').include? '/usr/local/bin'
  puts "Now try: brew help"
else
  opoo "/usr/local/bin is not in your PATH"
end