Script to allow for some fancy git workflows as described in https://wchargin.github.io/posts/managing-dependent-pull-requests/. I've extended it to also have features to support a style described in https://jg.gg/2018/09/29/stacked-diffs-versus-pull-requests/ via the --pick(-p) option

git-push-to-target.sh

#!/bin/sh
#
# git-push-to-target: Force push with lease this commit to a branch specified in its
# commit description like `branch: jake/my-branch`:
#
# `git-push-to-target --query` will do a dry run and print the branch name it detects
# `git-push-to-target --pick` will pick this to it's own branch off master and push.
#
# Usage within an interative rebase, add this after each commit that contains the branch directive:
# > exec git push-to-target
#
# Copyright (c) 2017 William Chargin. Released under the MIT license.
# https://wchargin.github.io/posts/managing-dependent-pull-requests/
# Modified by Jake Craige for:
#   - Mac sed support
#   - Remove branch prefix
#   - Support sha argument
#   - Support pick option to move to it's own branch

set -eu

DIRECTIVE='branch'

target_branch() {
  source="$1"
  directive="$( \
    git show "$source" --pretty='%B' \
    | sed -n 's/^'"${DIRECTIVE}"': \([A-Za-z0-9_./-]*\)$/\1/p' \
    ; )"
  if [ -z "${directive}" ]; then
    printf >&2 'error: missing "%s" directive\n' "${DIRECTIVE}"
    return 1
  fi
  if [ "$(printf '%s\n' "${directive}" | wc -l)" -gt 1 ]; then
    printf >&2 'error: multiple "%s" directives\n' "${DIRECTIVE}"
    return 1
  fi
  printf '%s\n' "${directive}"
}

main() {
  arg="${1:-none}"
  
  case $arg in
    -q|--query)
      branch="$(target_branch "${2:-HEAD}")"
      echo $branch
      return
      ;;
    -p|--pick)
      source="${2:-HEAD}"
      head_sha="${2:-$(git rev-parse --verify HEAD)}"
      branch="$(target_branch "$source")"

      set -x
      git fetch
      # create new branch from master, expect it to not exist or fail. tmp prefix needed to not
      # accidentally checkout an existing remote branch with same name.
      git checkout -b "tmp/$branch" origin/master
      # cherry-pick commit over and push the branch
      git cherry-pick "$head_sha"
      git push --force-with-lease origin HEAD:refs/heads/"$branch"

      # Clean up. Go back to where we came from. If specific commit sha given, assume no rebase and
      # go back to last branch. If not, we assume rebase and go back to the sha.
      # Then delete tmp branch from local git
      if [ -n "${2:-}" ]; then # non-empty value
        git checkout -
      else
        git checkout "$head_sha"
      fi
      git branch -D "tmp/$branch"
      ;;
    *)
      source="${1:-HEAD}"
      branch="$(target_branch "$source")"
      git push --force-with-lease origin "$source":refs/heads/"$branch"
      ;;
  esac
}

main "$@"