gistfile1.rb

#!/usr/bin/env ruby
require 'rubygems'

['json', 'cloudapp_api'].each do |gem|
  begin
    require gem
  rescue LoadError
    puts "You need to install #{gem}: gem install #{gem}"
    exit!(1)
  end
end

config_file = "#{ENV['HOME']}/.cloudapp"
unless File.exist?(config_file)
  puts "You need to type your email and password (one per line) into "+
       "`~/.cloudapp`"
  exit!(1)
end

email,password = File.read(config_file).split("\n")

if ARGV[0].nil?
   puts "You need to specify a file to upload."
   exit!(1)
end

urls = []
ARGV.each do |x|
  CloudApp.authenticate(email,password)
  puts "Attempting to upload #{x}"
  url = CloudApp::Item.create(:upload, {:file => x}).url

  # Say it for good measure.
  puts "Uploaded #{x} to #{url}"

  # Get the embed link.
  url = "#{url}/#{ARGV[0].split('/').last}"
  urls << url
end

# Copy it to your (linux) clipboard.
system %Q{echo '#{urls.join(',')}' | tr -d "\n" | xclip -i}

Changing the last line to this:

system %Q{echo '#{urls.join(',')}' | tr -d "\n" | ((which xclip >/dev/null && xclip -i) || (which xsel >/dev/null && xsel -b))}

Makes it work with either xclip or xsel.