Using git filter-branch for specific commits

Question

I'm trying to use the git filter-branch feature to remove a file that was recently updated and committed. I tried running the following command:

git filter-branch --force --index-filter 'git rm --cached --ignore-unmatch myfile' --prune-empty --tag-name-filter cat -- 6f7fda9..HEAD

However this only removes the file from the master branch, and I want it removed from all branches.

Starting with commit 6f7fda9 to HEAD I want the file removed. Is the command I'm running wrong?

Answer 1

Your requirements as stated are contradictory. Specifically

I want it removed from all branches.

and

Starting with commit 6f7fda9 to HEAD I want the file removed.

need to be reconciled. I suspect this comes down to an inaccurate understanding of commit ranges - which are only sort-of a thing in git.

Consider this commit graph:

x -- 6f7fda9 -- A -- B -- C -- F <--(master)
                 \                        ^(HEAD)
                  D -- E <--(branch)

So HEAD is at master which is at F; and there's a branch which was (apparently) created from A (after 6f7fda9 but before HEAD).

Now the question is, given this graph what does 6f7fda9..HEAD mean? And unfortunately, the answer isn't what a lot of people intuitively think.

6f7fda9..HEAD is short for HEAD ^6f7fda9 - meaning "everything reachable from HEAD but not reachable from 6f7fda9". "Reachable" means "the commit itself, and any commits you find by following parent pointers". So in this case, it means A, B, C, and F; but not x or 6f7fda9 (because they're reachable from 6f7fda9) and also not D, or E (because they aren't reachable from HEAD).

There are several ways to get filter-branch to process all the branches. For example you could

git filter-branch --force --index-filter 'git rm --cached --ignore-unmatch myfile' --prune-empty --tag-name-filter cat -- --all

But this will include all refs (not just all branches); if that's a problem

git filter-branch --force --index-filter 'git rm --cached --ignore-unmatch myfile' --prune-empty --tag-name-filter cat -- --branches

One other caveat - if you specifically don't want commits before 6f7fda9 rewritten, then you need to include one or more negative commit references. But assuming you do intend to include 6f7fda9 itself, you'd exclude its parent (not itself).

git filter-branch --force --index-filter 'git rm --cached --ignore-unmatch myfile' --prune-empty --tag-name-filter cat -- ^6f7fda9^ --branches

If 6f7fda9 is a merge, you'd have to list negative commit references for each of its parents.