Shell script for amending commits on a feature branch.

git-edit.sh

#!/bin/zsh

if [ "$1" = '-h' ]; then
	cat <<-EOF
Usage: git-edit <branch> [args-to-commit]

e.g. If your tree looks like this:
  * cc3cd23 (HEAD -> feat1) Feature 1.2
  * 53f56c1 Feature 1
  * 08355e5 (master) Initial commit.

And you want to change something from the commit "Feature 1",
  $ git checkout 53f56c1
  # Make your edits.
  $ git-edit feat1 --no-edit

You'll end up on the newly-amended version of 53f56c1, with the rest
of branch feat1 on top of you.
EOF
	exit 0
fi

# Exit when any command returns a non-zero exit code.
set -e

[ -z "$1" ] && (echo "No branch specified. Run with -h."; false)
original_commit=$(git rev-parse HEAD)
current_branch="$1"
shift

git commit --amend "$@"
new_commit=$(git rev-parse HEAD)
git rebase --onto $new_commit $original_commit "$current_branch"
git checkout --quiet $new_commit