cherry-pick merge commit (and its ancestors from merged branch)

git-cherry-pick-merge.sh

#!/bin/bash

set -e

USAGE=$(cat <<"EOF"
Usage:
    git-cherry-pick-merge <destination_branch> <merge_commit_ref>
    git-cherry-pick-merge --continue

Cherry-pick a merge commit (and its ancestors from the merged branch) onto
<destination_branch>, keeping the merge commit intact.

It is possible that a rebase failure will prevent this process from being
completely automatic. You will have to complete the rebase manually and run
`git-cherry-pick-merge --continue`.
EOF
)

if [ -z "$1" -o "$1" = "--help" -o "$1" = "help" ]; then
    echo "$USAGE"
    exit 0
fi

is_in_continue_mode=0
if [ "$1" = "--continue" ]; then
    is_in_continue_mode=1
fi

base_branch="$1"
merge_commit="$2"
tmp_merge_branch="tmp-merge-branch___${base_branch}___${merge_commit}"
if [ "$is_in_continue_mode" -eq "1" ]; then
    tmp_merge_branch=`git branch | grep \* | cut -d ' ' -f 2`
    # Ugh, it's just easier to use a real scripting language to split a string
    base_branch=`python -c "print('${tmp_merge_branch}'.split('___')[1])"`
    merge_commit=`python -c "print('${tmp_merge_branch}'.split('___')[2])"`
fi

merge_commit_msg=`git show -s --format=%B "$merge_commit"`

if [ "$is_in_continue_mode" -eq "0" ]; then
    git fetch
    git checkout -b "$tmp_merge_branch" "$merge_commit"
    git rebase --onto "origin/${base_branch}" "${merge_commit}^1" "$tmp_merge_branch" || {
        echo -e "==============================\n\nFinish your rebase manually and run \"git-cherry-pick-merge --continue\"\n"
        exit 1
    }
fi

git checkout "$base_branch"
git pull
git merge --no-ff "$tmp_merge_branch" -m "$merge_commit_msg" -e
git branch -D "$tmp_merge_branch"