rnag/.Rewrite-Git-Commit-Author.md

## .Rewrite-Git-Commit-Author.md

      
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              .Rewrite-Git-Commit-Author.md
            
          
    Bash/Zsh Function to Change Author for Commit(s)
Based off my Answer on SO.

The below function cca (shorthand for change-commit-author) makes some assumptions:

The branch with commit(s) to update author for is the current branch.
Git User / Email (AKA New Author) is the one currently set up with git.
One of the following arguments is passed in:

Email, to rewrite author of all commits under that email.
Space-separated list of Git Commit SHA(s), to change the author of.


Git commit signature verification is desired, and SSH/GPG keys are set up for that purpose (I made a script for this in case it is helpful).

Warning
Do not use in the main branch of shared or published projects without confirming
with other collaborators beforehand.
The reason is this script performs some "destructive" actions:

It rewrites all commit history, so if someone is working on a dev branch, they will have to rebase or else merge the changes of your branch into theirs.
If other collaborators and authors use commit signature verification as outlined above, their commits will likely say "Verified".
After running this script, all commits by other authors will say
"Unverified" -- since the script effectively "rewrites" commit history -- and they will need to run a script to
batch re-sign all their previous commits, which will likely
rewrite commit history again when changes are pushed.


## .zshrc
# Bash/Zsh Function to Change Author for Commit(s)
#
# Adapted from:
#
#   - https://stackoverflow.com/a/28845565/10237506
#   - https://docs.github.com/en/enterprise/2.18/user/github/using-git/changing-author-info
#
# Directions:
#
#    Enter either an *Email* to rewrite author of all commits by that email,
#    or a space-separated list of *Git Commit SHA(s)* to change the author of.
#
#    Examples:
#        cca old@email.org
#        cca sha-1 sha-2
#
#   To find Commit SHAs for a Git User with email `current@email.org`, use:
#
#       $ git --no-pager log --format=format:%H --author='current@email.org'
#
#   Alternatively, navigate to below link (substituting org, repo,
#   and Git author) and then *Click "Copy"*
#
#       https://github.com/ORG/REPO/commits?author=AUTHOR
#
function cca() {
    NUM_ARGS=$#

    if [ $NUM_ARGS -eq 0 ]; then
        echo "Usage: $0 <AUTHOR_EMAIL_OR_COMMIT_SHA_LIST...>"
        echo
        echo "Bash/Zsh Function to Change Author for Commit(s)"
        echo
        echo Function requires one or more arguments.
        echo
        echo Enter either an email to rewrite author of all commits by that email,
        echo "or a space-separated list of Git Commit SHA(s) to change the author of."
        echo
        echo Examples:
        echo "  $ $0 old@email.org"
        echo "  $ $0 abc123 xyz321"
        echo
        echo To find all Commit SHAs for a Git User with email \`current@email.org\`, use:
        echo "  $ git --no-pager log --format=format:%H --author='current@email.org'"
        return 1
    fi

    # Current Branch
    GIT_BRANCH=$(git rev-parse --abbrev-ref HEAD)
    GIT_NAME=$(git config --get user.name)
    GIT_EMAIL=$(git config --get user.email)

    echo "Branch:      ${GIT_BRANCH}"
    echo "Name:        ${GIT_NAME}"
    echo "Email:       ${GIT_EMAIL}"

    # Fix for error message from `git filter-branch`:
    #   Cannot create a new backup.
    #   A previous backup already exists in refs/original/
    #   Force overwriting the backup with -f
    #
    # Ref: https://stackoverflow.com/a/7654880/10237506
    git for-each-ref --format="%(refname)" refs/original/ | xargs -n 1 git update-ref -d

    # Check for ONE argument, and that the argument is an EMAIL
    # Partial Credits: https://stackoverflow.com/a/4501833/10237506
    if [[ $NUM_ARGS -eq 1 && "$1" =~ .+@.+ ]]; then

        GIT_OLD_EMAIL="$1"

        echo "Old Email:   ${GIT_OLD_EMAIL}"
        echo '[ Replacing Commit Author - Old Email > Email ]'

        # To change the name and/or email address recorded in existing commits,
        # you must rewrite the entire history of your Git repository.
        #
        # Credits: https://docs.github.com/en/enterprise/2.18/user/github/using-git/changing-author-info
        FILTER_BRANCH_SQUELCH_WARNING=1 \
            GIT_OLD_EMAIL="$GIT_OLD_EMAIL" \
            GIT_NAME="$GIT_NAME" \
            GIT_EMAIL="$GIT_EMAIL" \
            git filter-branch --env-filter '
        if [ "$GIT_COMMITTER_EMAIL" = "$GIT_OLD_EMAIL" ]
        then
        export GIT_COMMITTER_NAME="$GIT_NAME"
        export GIT_COMMITTER_EMAIL="$GIT_EMAIL"
        fi
        if [ "$GIT_AUTHOR_EMAIL" = "$GIT_OLD_EMAIL" ]
        then
        export GIT_AUTHOR_NAME="$GIT_NAME"
        export GIT_AUTHOR_EMAIL="$GIT_EMAIL"
        fi
        ' \
            --commit-filter '
        if [[ "$GIT_COMMITTER_EMAIL" = "$GIT_NAME" || "$GIT_AUTHOR_EMAIL" = "$GIT_EMAIL" ]]
        then
        git commit-tree -S "$@";
        fi
        ' \
            --tag-name-filter cat \
            -- --branches --tags

    else

        # Checkout the commit we are trying to modify
        #
        # The `-c advice.detachedHead=false` parameter will allow you to suppress the warning.
        # Ref: https://stackoverflow.com/a/45652159/10237506

        for GIT_COMMIT_SHA in "$@"; do

            git -c advice.detachedHead=false checkout "${GIT_COMMIT_SHA}"

            # Make the author change (use `--no-edit` to skip prompt to update commit message)
            #
            # Update to use `--reset-author` as mentioned in below, so we can also
            # set Git committer instead of just the author. Also, use existing committed date.
            #
            # Refs:
            #   - https://stackoverflow.com/a/74856838/10237506
            #   - https://stackoverflow.com/a/61217637/10237506
            git \
                -c user.name="${GIT_NAME}" \
                -c user.email="${GIT_EMAIL}" \
                commit -S \
                --amend \
                --reset-author \
                --no-edit \
                --date="$(git --no-pager log -1 --format='%aD')"

            GIT_NEW_COMMIT_SHA=$(git --no-pager log -1 --format="%H")

            # Checkout the original branch
            git checkout "${GIT_BRANCH}"

            echo "Commit SHA:        ${GIT_COMMIT_SHA}"
            echo "Commit SHA (NEW):  ${GIT_NEW_COMMIT_SHA}"

            # Replace the old commit with the new one locally
            git replace "${GIT_COMMIT_SHA}" "${GIT_NEW_COMMIT_SHA}"

        done

        # Rewrite all commits based on the replacement
        #
        # Also, sign the commits authored by this user if possible,
        # and correct committer date for rewritten commit above.
        #
        # Refs:
        #   - https://stackoverflow.com/a/41883164/10237506
        #   - https://stackoverflow.com/a/24820045/10237506

        FILTER_BRANCH_SQUELCH_WARNING=1 \
            GIT_NAME=$GIT_NAME \
            GIT_EMAIL=$GIT_EMAIL \
            git filter-branch \
            --env-filter \
            'export GIT_COMMITTER_DATE="$GIT_AUTHOR_DATE"' \
            --commit-filter '
        if [[ "$GIT_COMMITTER_EMAIL" = "$GIT_NAME" || "$GIT_AUTHOR_EMAIL" = "$GIT_EMAIL" ]]
        then
        git commit-tree -S "$@";
        else
        git commit-tree "$@";
        fi
        ' \
            -- --all

        # Remove the replacement for cleanliness
        for GIT_COMMIT_SHA in "$@"; do
            git replace -d "${GIT_COMMIT_SHA}"
        done

    fi

    # Seems to be needed for `--force-with-lease` to work!
    git fetch

    # Push the new history
    if ! git push --force-with-lease; then
        # Only use `--force` instead of `--force-with-lease`
        # if the latter fails, and only after sanity checking
        # with git log and/or git diff.
        echo 'Git Push with `--force-with-lease` failed.'
        # Ref: https://stackoverflow.com/a/14741036/10237506
        if git diff --exit-code && [[ -z $(git status -uno --porcelain) ]]; then
            echo Git Status/Diff - OK
            N=5
            echo [ Git Log - Showing Top ${N} Commits ]
            git --no-pager log --graph --pretty=format:'%Cred%h%Creset -%C(yellow)%d%Creset %s %Cgreen(%cr) %C(bold blue)<%an>%Creset' --abbrev-commit -n ${N}
            echo

            # Confirm w/ user to use `--force` for `git push`
            printf '%s' 'Proceed with `git push --force`? [y/N] '

            # Read Character, compatible with `zsh` and `bash`
            # https://stackoverflow.com/a/30022297/10237506
            read_char() {
                stty -icanon -echo
                eval "$1=\$(dd bs=1 count=1 2>/dev/null)"
                stty icanon echo
            }

            read_char REPLY

            echo "$REPLY" # (optional) move to a new line
            if [[ $REPLY =~ ^[Yy]$ ]]; then
                git push -f
                echo 'Git Push with `--force` successful!'
            fi
        else
            echo Git Status/Diff - ERROR, aborting.
            return 1
        fi
    else
        echo 'Git Push with `--force-with-lease` successful!'
    fi
}
	# Bash/Zsh Function to Change Author for Commit(s)
	#
	# Adapted from:
	#
	# - https://stackoverflow.com/a/28845565/10237506
	# - https://docs.github.com/en/enterprise/2.18/user/github/using-git/changing-author-info
	#
	# Directions:
	#
	# Enter either an Email to rewrite author of all commits by that email,
	# or a space-separated list of Git Commit SHA(s) to change the author of.
	#
	# Examples:
	# cca old@email.org
	# cca sha-1 sha-2
	#
	# To find Commit SHAs for a Git User with email `current@email.org`, use:
	#
	# $ git --no-pager log --format=format:%H --author='current@email.org'
	#
	# Alternatively, navigate to below link (substituting org, repo,
	# and Git author) and then Click "Copy"
	#
	# https://github.com/ORG/REPO/commits?author=AUTHOR
	#
	function cca() {
	NUM_ARGS=$#

	if [ $NUM_ARGS -eq 0 ]; then
	echo "Usage: $0 <AUTHOR_EMAIL_OR_COMMIT_SHA_LIST...>"
	echo
	echo "Bash/Zsh Function to Change Author for Commit(s)"
	echo
	echo Function requires one or more arguments.
	echo
	echo Enter either an email to rewrite author of all commits by that email,
	echo "or a space-separated list of Git Commit SHA(s) to change the author of."
	echo
	echo Examples:
	echo " $ $0 old@email.org"
	echo " $ $0 abc123 xyz321"
	echo
	echo To find all Commit SHAs for a Git User with email \`current@email.org\`, use:
	echo " $ git --no-pager log --format=format:%H --author='current@email.org'"
	return 1
	fi

	# Current Branch
	GIT_BRANCH=$(git rev-parse --abbrev-ref HEAD)
	GIT_NAME=$(git config --get user.name)
	GIT_EMAIL=$(git config --get user.email)

	echo "Branch: ${GIT_BRANCH}"
	echo "Name: ${GIT_NAME}"
	echo "Email: ${GIT_EMAIL}"

	# Fix for error message from `git filter-branch`:
	# Cannot create a new backup.
	# A previous backup already exists in refs/original/
	# Force overwriting the backup with -f
	#
	# Ref: https://stackoverflow.com/a/7654880/10237506
	git for-each-ref --format="%(refname)" refs/original/ \| xargs -n 1 git update-ref -d

	# Check for ONE argument, and that the argument is an EMAIL
	# Partial Credits: https://stackoverflow.com/a/4501833/10237506
	if [[ $NUM_ARGS -eq 1 && "$1" =~ .+@.+ ]]; then

	GIT_OLD_EMAIL="$1"

	echo "Old Email: ${GIT_OLD_EMAIL}"
	echo '[ Replacing Commit Author - Old Email > Email ]'

	# To change the name and/or email address recorded in existing commits,
	# you must rewrite the entire history of your Git repository.
	#
	# Credits: https://docs.github.com/en/enterprise/2.18/user/github/using-git/changing-author-info
	FILTER_BRANCH_SQUELCH_WARNING=1 \
	GIT_OLD_EMAIL="$GIT_OLD_EMAIL" \
	GIT_NAME="$GIT_NAME" \
	GIT_EMAIL="$GIT_EMAIL" \
	git filter-branch --env-filter '
	if [ "$GIT_COMMITTER_EMAIL" = "$GIT_OLD_EMAIL" ]
	then
	export GIT_COMMITTER_NAME="$GIT_NAME"
	export GIT_COMMITTER_EMAIL="$GIT_EMAIL"
	fi
	if [ "$GIT_AUTHOR_EMAIL" = "$GIT_OLD_EMAIL" ]
	then
	export GIT_AUTHOR_NAME="$GIT_NAME"
	export GIT_AUTHOR_EMAIL="$GIT_EMAIL"
	fi
	' \
	--commit-filter '
	if [[ "$GIT_COMMITTER_EMAIL" = "$GIT_NAME" \|\| "$GIT_AUTHOR_EMAIL" = "$GIT_EMAIL" ]]
	then
	git commit-tree -S "$@";
	fi
	' \
	--tag-name-filter cat \
	-- --branches --tags

	else

	# Checkout the commit we are trying to modify
	#
	# The `-c advice.detachedHead=false` parameter will allow you to suppress the warning.
	# Ref: https://stackoverflow.com/a/45652159/10237506

	for GIT_COMMIT_SHA in "$@"; do

	git -c advice.detachedHead=false checkout "${GIT_COMMIT_SHA}"

	# Make the author change (use `--no-edit` to skip prompt to update commit message)
	#
	# Update to use `--reset-author` as mentioned in below, so we can also
	# set Git committer instead of just the author. Also, use existing committed date.
	#
	# Refs:
	# - https://stackoverflow.com/a/74856838/10237506
	# - https://stackoverflow.com/a/61217637/10237506
	git \
	-c user.name="${GIT_NAME}" \
	-c user.email="${GIT_EMAIL}" \
	commit -S \
	--amend \
	--reset-author \
	--no-edit \
	--date="$(git --no-pager log -1 --format='%aD')"

	GIT_NEW_COMMIT_SHA=$(git --no-pager log -1 --format="%H")

	# Checkout the original branch
	git checkout "${GIT_BRANCH}"

	echo "Commit SHA: ${GIT_COMMIT_SHA}"
	echo "Commit SHA (NEW): ${GIT_NEW_COMMIT_SHA}"

	# Replace the old commit with the new one locally
	git replace "${GIT_COMMIT_SHA}" "${GIT_NEW_COMMIT_SHA}"

	done

	# Rewrite all commits based on the replacement
	#
	# Also, sign the commits authored by this user if possible,
	# and correct committer date for rewritten commit above.
	#
	# Refs:
	# - https://stackoverflow.com/a/41883164/10237506
	# - https://stackoverflow.com/a/24820045/10237506

	FILTER_BRANCH_SQUELCH_WARNING=1 \
	GIT_NAME=$GIT_NAME \
	GIT_EMAIL=$GIT_EMAIL \
	git filter-branch \
	--env-filter \
	'export GIT_COMMITTER_DATE="$GIT_AUTHOR_DATE"' \
	--commit-filter '
	if [[ "$GIT_COMMITTER_EMAIL" = "$GIT_NAME" \|\| "$GIT_AUTHOR_EMAIL" = "$GIT_EMAIL" ]]
	then
	git commit-tree -S "$@";
	else
	git commit-tree "$@";
	fi
	' \
	-- --all

	# Remove the replacement for cleanliness
	for GIT_COMMIT_SHA in "$@"; do
	git replace -d "${GIT_COMMIT_SHA}"
	done

	fi

	# Seems to be needed for `--force-with-lease` to work!
	git fetch

	# Push the new history
	if ! git push --force-with-lease; then
	# Only use `--force` instead of `--force-with-lease`
	# if the latter fails, and only after sanity checking
	# with git log and/or git diff.
	echo 'Git Push with `--force-with-lease` failed.'
	# Ref: https://stackoverflow.com/a/14741036/10237506
	if git diff --exit-code && [[ -z $(git status -uno --porcelain) ]]; then
	echo Git Status/Diff - OK
	N=5
	echo [ Git Log - Showing Top ${N} Commits ]
	git --no-pager log --graph --pretty=format:'%Cred%h%Creset -%C(yellow)%d%Creset %s %Cgreen(%cr) %C(bold blue)<%an>%Creset' --abbrev-commit -n ${N}
	echo

	# Confirm w/ user to use `--force` for `git push`
	printf '%s' 'Proceed with `git push --force`? [y/N] '

	# Read Character, compatible with `zsh` and `bash`
	# https://stackoverflow.com/a/30022297/10237506
	read_char() {
	stty -icanon -echo
	eval "$1=\$(dd bs=1 count=1 2>/dev/null)"
	stty icanon echo
	}

	read_char REPLY

	echo "$REPLY" # (optional) move to a new line
	if [[ $REPLY =~ ^[Yy]$ ]]; then
	git push -f
	echo 'Git Push with `--force` successful!'
	fi
	else
	echo Git Status/Diff - ERROR, aborting.
	return 1
	fi
	else
	echo 'Git Push with `--force-with-lease` successful!'
	fi
	}