Turn Time Machine ON

sudo tmutil enable

Turn Time Machine OFF

sudo tmutil disable

If you want to exclude a file or folder, like a users Downloads:

sudo tmutil addexclusion ~/Downloads

The tmutil addexclusion command has an interesting property: it’s sticky. When you use this command, the item you exclude remains in the Time Machine exclusion list even if you move it, which is not the case when you exclude items from the Time Machine preference pane. If you use the above command with the -p flag, then it will not be sticky, and will be the same as an exclusion you add from the Time Machine preference pane.

To know if a file or folder is excluded, run this for an answer and your output will be [Excluded]:

tmutil isexcluded ~/Downloads/

Get info on where backups are stored:

tmutil destination info

You can use this to find the OS default exclusion list, this is not however what has manually been excluded:

sudo mdfind "com_apple_backup_excludeItem = 'com.apple.backupd'"