Setup SSH login without a password.

auto-ssh.rb

#!/usr/bin/env ruby
#
# auto-ssh.rb - Setup SSH login without a password.
# Made with ❤︎ by [email protected]

## Gem Installer
def require_gems(*gems)
  gems.each do |_gem|
    begin require _gem
      rescue LoadError
        dep = _gem.split('/')[0]
        puts "[Info] Installing the dependency '#{dep}'."
        system("gem install #{dep} > /dev/null 2>&1")
        require _gem
    end
  end
end

## Version, Require Stuff, & Clean Exit
version = 0.3
Signal.trap("INT") { puts; exit 0 }
require_gems( 'optparse', 'io/console', 'net/sftp' )

## Get CLI Options
opt_parser = OptionParser.new do |opts|
  opts.banner = "Usage: #{$0} [flag]"
  opts.on("--help", "Show this message.") do
    puts opts
    exit
  end
  opts.on("-h", "--host HOSTNAME", "The remote host to install your public key.") do |hn|
    @host = hn
  end
  opts.on("-u", "--user USERNAME", "The user to log into the remote host.")       do |un|
    @user = un
  end
  opts.on("-p", "--pass PASSWORD", "The password to log into the remote host.")   do |pw|
    @pass = pw
  end
  opts.on("-k", "--key KEYFILE",   "The path to the public key to install.")      do |kf|
    @key  = kf
  end
end

## Parse Options
begin opt_parser.parse! ARGV
rescue OptionParser::InvalidOption => e
  puts "[Error] #{e}"
  exit 1
rescue OptionParser::MissingArgument => e
  puts "[Error] #{e}"
  exit 1
end

## Ask about remote system.
puts "I need some information about the remote system."
@host ||= (print 'Hostname: '; gets.chomp)
@user ||= (print 'Username: '; gets.chomp)
@pass ||= (print 'Password: '; $stdin.noecho(&:gets).chomp)
puts

## Get this users key.
def get_key
  # If the key was set from an argument, lets read it.
  unless @key.nil?
    puts "Reading your public key."
    @key = File.read(@key)
    return
  end
  
  # Let's generate a key if one does not already exist.
  unless File.exists?(File.expand_path('~/.ssh/id_rsa.pub'))
    puts "You don't have a rsa key pair yet. So I will generate one for you."
    `ssh-keygen -t rsa`
  end
  
  # We can now read the public key.
  puts "Reading your public key."
  @key = File.read(File.expand_path('~/.ssh/id_rsa.pub'))
  
end

## Give remote host this users key.
def write_key
  puts "Accessing the remote host '#{@host}'."
  begin
    Net::SFTP.start(@host, @user, :password => @pass) do |sftp|
      puts "Creating the SSH directory on '#{@host}'."
      sftp.mkdir! '.ssh'
      
      puts "Adding your key to #{@user}@#{@host}'s authorized keys."
      sftp.file.open('.ssh/authorized_keys', 'a') do |f|
        f.puts @key
      end
    end
  rescue SocketError
    abort('[Error] The port was not open on the remote host.')
  rescue Timeout::Error
    abort('[Error] The connection timed out.')
  rescue Errno::EHOSTUNREACH
    abort('[Error] Could not reach the remote host.')
  rescue Errno::ECONNREFUSED
    abort('[Error] The connection to the remote host was refused.')
  rescue Net::SSH::AuthenticationFailed
    abort('[Error] Authentication with the remote host failed.')
  rescue NameError
    abort('[Error] The gem "net-sftp" is not installed.')
  rescue Exception
    abort('[Error] An unknown error occurred.')
  end
end

## Run Actions
get_key
write_key
puts "You can now login to #{@host} without a password."