This seems to have nothing to do with perl... but I'll bite.

system('scp login:password@host:path/to/file.txt file_backup.txt');
if (-f 'file_backup.txt')
{
    system('ssh login:password@host rm path/to/file.txt');
}
[download]

More safeguards are necessary here, and I shudder to see a password in plaintext. Learn to use ssh's authorized_keys file at the minimum. Reading all of ssh's manpage until enlightenment comes is better.