Ignoring an already checked-in directory's contents?

I have a git repository that's used only to hold graphics and sound files used in several projects. They are all in one directory without sub-directories. Now I just created a script to copy these assets over from another, structured directory, with several levels of sub-directories.

Now I only want the (source) hierarchical file structure to be tracked by git, and the (target) flat directory (with all the files in one pile) should be ignored.

I've added the target directory to .gitignore, but git is still tracking changes in it. I thought if I commit the deletion of the old file in the target directory, git might stop tracking the new contents (copied in by the script), but it doesn't.

How do I make git forget about the target directory?

This command will cause git to untrack your directory and all files under it without actually deleting them:

git rm -r --cached <your directory>

The -r option causes the removal of all files under your directory.

The --cached option causes the files to only be removed from git's index, not your working copy. By default git rm <file> would delete <file>.

If you need to have a tracked file (checked in), but do not want to track further changes of a file while keeping it in your local repository as well as in the remote repository, this can be done with:

git update-index --assume-unchanged path/to/file.txt

After that any changes to this file will no longer show up in git status.

For a subdirectory called blah/ added to git, both of the following seem to work to ignore new files in blah/. Added to .gitignore:

blah 
blah/*