git-retime: edit the timestamp of the HEAD commit

git-retime.sh

#!/bin/sh

set -e

USAGE=''
SUBDIRECTORY_OK=1

. "$(git --exec-path)/git-sh-setup"

if [ $# -gt 0 ]
then
    usage
fi

date_file="$GIT_DIR/GIT_RETIME"

# Ensure only one instance of git-retime is running at a time
if ( set -o noclobber; echo 'locked' > "$date_file" ) 2>/dev/null
then
    # Ensure the lock file is deleted on exit
    trap "rm -f \"$date_file\"; exit $?" 0
    # Write the existing date to the file
    git show -s --format='%ad' > "$date_file"
    echo "# Please edit the timestamp above. Lines starting with '#' are ignored," >> "$date_file"
    echo "# and an empty date aborts the retime." >> "$date_file"
    # Open an editor
    git_editor "$date_file"
    # Remove comment lines
    # We need '|| true' here, because grep returns non-zero status on empty files
    new_date="$(grep -v '^#' "$date_file" || true)"
    if [ "z$new_date" != 'z' ]
    then
        # Amend the commit with the new date
        GIT_COMMITTER_DATE="$new_date" \
            git commit --amend --date="$new_date" --no-edit
    else
        echo 'aborting retime due to empty timestamp'
    fi
else
    die 'cannot obtain lock (is git-retime already running?)'
fi