Say I have:

    $> git remote
    Alpha
    Beta
    Gamma
    Delta

It is easy to sync with all repos via:

    $> git annex sync

Or specific repos via:

    $> git annex sync Alpha Beta

However, it is currently awkward to exclude specific repos. Is it possible to 'invert' or 'negate' specific remotes, so that the following are equivalent?

    $> git annex sync \! Gamma
    $> git annex sync Alpha Beta Delta

This problem comes up surprisingly often due to:

  1. An external host being temporarily down (which causes sync to hang for a while),
  2. Repos being available, but the machine is under heavy IO load or memory pressure,
  3. Repos on external drives that are swapped out and mounted to a specific location (e.g., /mnt/),
  4. Wanting to roll out repo-wide changes in stages, or keeping 1-2 repos untouched for whatever reason, or
  5. Some repos being too large for a machine (e.g., repacking fails due to low memory), but which can still act like a dumb file-store.

The problem gets worse when you have a lot of remotes or a lot of repos to manage (I have both). My impression is that this feature would require a syntax addition for git-annex-sync only. I like '!' because it behaves the same in GNU find and sh.
