Git – Difference Between ‘assume-unchanged’ and ‘skip-worktree’

You want skip-worktree.

assume-unchanged is designed for cases where it is expensive to check whether a group of files have been modified; when you set the bit, git (of course) assumes the files corresponding to that portion of the index have not been modified in the working copy. So it avoids a mess of stat calls. This bit is lost whenever the file’s entry in the index changes (so, when the file is changed upstream).

skip-worktree is more than that: even where git knows that the file has been modified (or needs to be modified by a reset --hard or the like), it will pretend it has not been, using the version from the index instead. This persists until the index is discarded.

There is a good summary of the ramifications of this difference and the typical use cases here: http://fallengamer.livejournal.com/93321.html .

From that article:

• --assume-unchanged assumes that a developer shouldn’t change a file. This flag is meant for improving performance for not-changing folders like SDKs.
• --skip-worktree is useful when you instruct git not to touch a specific file ever because developers should change it. For example, if the main repository upstream hosts some production-ready configuration files and you don’t want to accidentally commit changes to those files, --skip-worktree is exactly what you want.