I use a simple lftp script to update Slack. Before that, I have been using a hacker-ish complex Bash script that didn't really live up to the efficiency of how lftp does mirroring.
lftp -f slack.lftp
# This is how you can do something with a one-liner but I require serveral
# operations that cannot be performed in one line. At least that's what I think.
# lftp -c open -e "mput *" username:paddword@hostname
mirror -e ftp://slackware.oregonstate.edu/pub/slackware/slackware-13.0/patches/packages ./13.0