install_gems.rb

#!/usr/bin/env ruby

# install_gems.rb

# Copyright 2009 Robert Jones jones@craic.com
# Use at your own risk, no warranty, etc, etc.

# Given a file of gems from another machine, recreate the same environment
# For more information see this post:
# http://craiccomputing.blogspot.com/2009/04/installing-ruby-19-and-gems-on-machine.html

# 1: Generate the list of gems with 'gem list' or 'gem list --no-versions'
# 2: Delete lines with any gems you don't want to mirror, or comment them out with
# a '#' in the first column
# 3: Transfer the file to the target machine
# 4: Run this script with the filename as the only argument (run as root)
#    If you want to install documentation then add the 'docs' option

# Capture the stderr output in a file for debugging

def already_installed(gem)
    result = `gem list --local --no-versions #{gem}`
    installed = false
    result.each_line do |str|
      if str =~ /^#{gem}\s/
        installed = true
        break
      end
    end
    installed
end

if ARGV.length < 1 or ARGV.length > 2
  STDERR.puts "Usage: #{$0} <list of gems> [docs]"  
  exit
end

doc_options = ARGV.length == 2 ? '' : ' --no-ri --no-rdoc'
filename = ARGV[0]

open(filename, 'r').each_line do |line|
  line.chomp!
  if line =~ /^\s*$/ or line =~ /^\*\*\*/ or line =~ /^#/
    next
  elsif line =~ /^(\S+)/
    gem = $1
    # Does the system already have this gem? - This won't pay attention to versions..
    installed = already_installed(gem)
    if not installed
      puts "Installing #{gem}\n"
      `gem install #{doc_options} #{gem} &> tmp_error_log`
      installed = already_installed(gem)
      if not installed # something went wrong
        puts "----------------------------------------------------------\nFAILED"
        open('tmp_error_log', 'r') { |f| puts f.read }
        File.delete('tmp_error_log')
        puts "----------------------------------------------------------\n"
      end
    else
      puts "Skipping #{gem}\n"   
    end
  end
end