git-set-author

#!/usr/bin/env bash
#
# Update the author of the last commit.
#
# Usage:
#
#     # 0 args ⟹ read author name and email from Git config
#     git set-author [-p|--preserve-committer-date]
#
#     # If 1 arg is provided:
#     # - If it contains a space, treat it as a name
#     # - If it matches an existing "ref" (branch/tag/SHA), copy author info from the corresponding commit
#     # - Otherwise, treat it as an email address
#     git set-author [-p|--preserve-committer-date] <name|email|ref>
#
#     # 2 args ⟹ name, email
#     git set-author [-p|--preserve-committer-date] <name> <email>

preserve_committer_date=
case "$1" in
    -p | --preserve-committer-date)
        preserve_committer_date=1
        shift
        ;;
esac

if [ $# -eq 0 ]; then
    name="$(git config user.name)"
    email="$(git config user.email)"
    author="$$name <$email>"
    echo "Setting author: $author" >&2
elif [ $# -eq 1 ]; then
    if [[ "$1" == *' '* ]]; then
        # If the argument has more than one word, assume it's the author's name.
        name="$1"; shift
        email="$(git log -1 --format=%ae)"
        author="$name <$email>"
        echo "Updating author name: $author" >&2
    elif git cat-file -t "$1" &>/dev/null; then
        # Otherwise, check whether it's a Git "ref", and copy that author name/email if so
        ref="$1"; shift
        author="$(git show -s --format='%an <%ae>' "$ref")"
        echo "Updating author from commit $ref: $author" >&2
    else
        # Otherwise, assume we're updating the author's email address
        email="$1"; shift
        name="$(git log -1 --format=%an)"
        author="$name <$email>"
        echo "Updating author email: $author" >&2
    fi
elif [ $# -eq 2 ]; then
    name="$1"; shift
    email="$1"; shift
    author="$name <$email>"
    echo "Setting author: $author" >&2
else
    echo "Usage: git set-author [-p|--preserve-committer-date] [name <email>]" >&2
    echo "Usage: git set-author [-p|--preserve-committer-date] <name> <email>" >&2
    exit 1
fi

if [ "$preserve_committer_date" ]; then
    GIT_COMMITTER_DATE="$(git log -1 --format=%cd)"
    export GIT_COMMITTER_DATE
    echo "Preserving committer date: $GIT_COMMITTER_DATE" >&2
fi

cmd=(git commit --amend --no-edit --allow-empty --author "$author")
echo "Running: ${cmd[*]}" >&2
"${cmd[@]}"