This script is used to download the latest file from the server to your local machine using Ruby & pem key

ruby_sftp_download.rb

#This script is used to download file from the server to your local machine
#The implementation is based on pure Ruby implementation of SFTP using gem Net SFTP
#To install this on your local machine please run the following command in your terminal 'gem install net-sftp'
#Author : Ashish Wadekar <ashishawadekar@gmail.com>
#Date : 18 December 2016

#This is the gem / library required for the SFTP connection management
require 'net/sftp'

#The host address
HOST = "www.example.com"

#User for connection
USER = "admin"

#The location of the authentication key in pem format
SERVER_KEY_LOC = "/location/of/serverauthenticationkey.pem"

#The location on server where DB backups are done
SERVER_BACKUP = "/location/of/file/on/server"

#The location on local machine where the db has to be downloaded
LOCAL_BACKUP = "/location/on/local/machine/where/file/needs/to/be/downloaded"

#Array to hold the file names for easier sorting
files = Array.new

#Array to hold the file details for easier sorting
files_details = Array.new

#Inititalising the connection
Net::SFTP.start(HOST, USER, :keys => [SERVER_KEY_LOC]) do |sftp|
  puts "Connection to Server successful"
  entries = sftp.dir.entries([SERVER_BACKUP]).sort_by(&:name) #Sorting the files by name as timestamp is used as filename
  entries.each do |entry|
    files << entry.name
    files_details << entry.longname
  end

  download_size = files_details[-1].split(' ')[4].to_i

  puts "Total #{(files.size.to_i) - 2} backups found on server."
  puts "The latest file is : #{files[-1]}, Size : #{(download_size)/1048576} MB"
  puts "Now donwloading the file to your local machine at path : #{LOCAL_BACKUP}"


  sftp.download!(SERVER_BACKUP+files[-1], LOCAL_BACKUP+files[-1]) do |event, downloader, *args|
    case event
    when :open then
      # args[0] : file metadata
      puts "Starting download from server: #{args[0].remote} -> #{args[0].local}"
      puts "Perhaps you can sip a coffee till then!"
    when :get then
      # args[0] : file metadata
      # args[1] : byte offset in remote file
      # args[2] : data that was received
      STDOUT.write "Downloading complete: #{args[1].to_i/1048576}MB, #{args[1].to_i}bytes of #{download_size} bytes, #{((args[1].to_i / download_size) * 100.0)}% \r" unless args[1].to_i == 0

    when :close then
      # args[0] : file metadata
      puts "Done! Closing connection to server."
    when :mkdir then
      # args[0] : local path name
      puts "Creating directory #{args[0]}"
    when :finish then
      puts "Backup download complete!"
    end
  end
end