Rename multiple names and emails in a single pass of git-filter-branch

Question

Is it possible to mass-rename 2 or more email addresses with a single pass of git filter-branch?

I tried adapting the code from this answer by just duplicating the if..fi clause:

git filter-branch --commit-filter '
        if [ "$GIT_COMMITTER_NAME" = "<Old Name 1>" ];
        then
                GIT_COMMITTER_NAME="<New Name 1>";
                GIT_AUTHOR_NAME="<New Name 1>";
                GIT_COMMITTER_EMAIL="<New Email 1>";
                GIT_AUTHOR_EMAIL="<New Email 1>";
                git commit-tree "$@";
        else
                git commit-tree "$@";
        fi
        if [ "$GIT_COMMITTER_NAME" = "<Old Name 2>" ];
        then
                GIT_COMMITTER_NAME="<New Name 2>";
                GIT_AUTHOR_NAME="<New Name 2>";
                GIT_COMMITTER_EMAIL="<New Email 2>";
                GIT_AUTHOR_EMAIL="<New Email 2>";
                git commit-tree "$@";
        else
                git commit-tree "$@";
        fi' HEAD

But it gave me errors during the filter-branch that looked like this:

error: duplicate parent bc8f9924c33558a275b8f694969529cf56232c80 ignored

And then the branch history was all tangled up:

Ectopia

Answer 1

You want just one git commit-tree command, after setting all the environment variables as desired. For instance, your commit filter might read something like this:

git filter-branch -f --commit-filter '
    if [ "$GIT_COMMITTER_NAME" = "<Old Name 1>" ]; then
        GIT_COMMITTER_NAME="<New Name 1>";
        GIT_AUTHOR_NAME="<New Name 1>";
        GIT_COMMITTER_EMAIL="<New Email 1>";
        GIT_AUTHOR_EMAIL="<New Email 1>";
    fi;
    if [ "$GIT_COMMITTER_NAME" = "<Old Name 2>" ]; then
        GIT_COMMITTER_NAME="<New Name 2>";
        GIT_AUTHOR_NAME="<New Name 2>";
        GIT_COMMITTER_EMAIL="<New Email 2>";
        GIT_AUTHOR_EMAIL="<New Email 2>";
    fi;
    git commit-tree "$@"
    '

(although if the number of name changes to make gets higher I'd probably run through a mapping file instead of a long series of easy-to-typo if ... thens, and it might make more sense to map author and committer separately).

Remember that filter-branch simply copies all the commits you tell it to copy (by using git commit-tree to make the new copy), while building a map of <old-sha1,new-sha1> pairs. This is why making two commits is not good: one existing (old) SHA-1 now has to map to two new copies, which is simply not allowed in terms of what filter-branch does with the commit graph. (Multiple old SHA-1s can map to a single new SHA-1, if you choose to omit some commits during the copying process. That is, the new graph can be bijective or surjective, but filter-branch doesn't really believe in injective, as it's going to try to map the old references to the new graph.)

Embellishment