rsync -av
rsync -av [--delete] [--dry-run] <from>/ <to>/
Risk: Careful
What it does
Makes a folder there match a folder here, sending only the changes.
When to use it
To update a website or a backup again and again.
Example
$ rsync -av site/ kedai:shop/Send what changed. The slash after site means its contents.
$ rsync -av --delete --dry-run site/ kedai:shop/Show what --delete would remove, and change nothing.
Learn it in: Copy files: scp and rsync · Official docs