How to verify the file after the FTP transfer???

Hi! I'm now stuck on how to verify the file after the FTP transfer. I'm writing a script that do the files and database backup and verifying them. I'm using the Unix machine. Since I'm using the tar utility via the shell environment in PHP, like PassThru() or Exec(). I'm using the tar utility via Exec() for backing up and verifying because it have a lot of tar's options that I can use. As for the FTP, I decided to do the Exec() for transfering and verifying. Now the only thing left is to verify it. I welcome your suggestion and thought on this... Thanks, Scott