An extremely case-specific implementation of git-filter-branch

rewrite-lg2s.sh

#!/bin/bash

# It's no libgit2, but it's pretty useful
. $(git --exec-path)/git-sh-setup

cd_to_toplevel
require_clean_work_tree

set -e

# git-sh-setup provides get_author_ident_from_commit but not this one, so let's just copy it
get_committer_ident_from_commit () {
        encoding=$(git config i18n.commitencoding || echo UTF-8)
        git show -s --pretty=raw --encoding="$encoding" "$1" -- |
        parse_ident_from_commit committer COMMITTER
}

clear_local_git_env

# Detach and put us on the first commit which doesn't get rewritten
git checkout -q -f 41bc8c6

# Now we need to put the other two on top, we take their tree and
# commit that, keeping their commiter ident intact as well

pick_one () {
    local active_commit="$1"
    clear_local_git_env
    eval $(get_author_ident_from_commit "$active_commit")
    eval $(get_committer_ident_from_commit "$active_commit")
    export GIT_COMMITTER_NAME GIT_COMMITTER_EMAIL GIT_COMMITTER_DATE
    git read-tree "$active_commit"
    git commit -q -C "$active_commit"
    clear_local_git_env
}

pick_one 6dcf9bf75
pick_one e90810b8d

git checkout -q -f
git checkout -q -B test

echo "There you go, boss, your rewritten test branch is at"
git rev-parse HEAD