FTP ... stands for File Transfer Protocol. You have a server which has directories that you can read files from or copy file to (Depending on you access).

By typing FTP at the shell (command line) you are starting a client that can "get" or "put" files on the server.

If you are looking at doing this Client stuff from within a script hardburn is correct look at Net::FTP. (Example from the docs below)

    #You have to tell your script to use the module.
    use Net::FTP;

     #Establish a connection to the ftp server (in this case some.host
+.name)
    $ftp = Net::FTP->new("some.host.name", Debug => 0)
      or die "Cannot connect to some.host.name: $@";

    #provide the login information to the ftp server
    $ftp->login("anonymous",'-anonymous@')
      or die "Cannot login ", $ftp->message;

    #Change dir to /pub
    $ftp->cwd("/pub")
      or die "Cannot change working directory ", $ftp->message;

    #copy the file from the ftp server to your local dir.
    $ftp->get("that.file")
      or die "get failed ", $ftp->message;

    #End your connection to the ftp server
    $ftp->quit;
[download]

If you are looking to write a "kind of" server you need to look at Net::FTPServer although I have had no experience with this.