Running filter-branch over a range of commits

Question

git filter-branch --env-filter \'
export GIT_AUTHOR_EMAIL=\"foo@example.com\"
export GIT_AUTHOR_NAME=\"foo\"\' -- commita..commitb

Results in

Answer 1

You cannot just override commits in a middle of a history, because sha1 of a commit depends on a parent's. So, the git doesn't know where do you want point your HEAD reference after the filtration. So, you should rewrite all up to the HEAD.

Example:

A---B---C---D---E---F   master
            \
             \--G---H   branch

if you want filter commits B and C you should also filter all commits after: D, E, F, G, H. So, that's why git tells you to use a ref at the end of the range, so that it just not finishes up with a detached head.

After you modify B and C commits and stop will look like this:

A---B---C---D---E---F   master
\           \
 \           \--G---H   branch
  \-B'--C'      (HEAD or a temporary TAG?..)      

So, the master and branch will be untouched. I don' think this is that you want. It means you must override all commits. The history will be then:

A---B---C---D---E---F   (loose end, will be garbage collected one day)
\           \
 \           \--G---H   (loose end, will be garbage collected one day)
  \-B'--C'--D'--E'--F'  master
            \
             \--G'--H'  branch