Copy a file or directory while preserving git line history

git-copy.sh

#!/bin/bash
# set -x  # turn on debugging
set -e  # exit on fail

########################################################################
#
# Copy a file or directory while preserving git line history
# Manually trim the files after to accomplish a split!
#
# Note: This script makes several commits to the current branch.
#   If you squash-merge these commits, line history will not be
#   preserved.
#
########################################################################

if [ -z "$1" ] || [ -z "$2" ]; then
    echo "Usage: $(basename "$0") ORIGNAL_FILE NEW_FILE"
    exit 1
fi

orig="$1"
copy="$2"
temp="temp"

# append "/" if these are dirs -- really, just needed for commit message(s)
if [ -d "$1" ]; then
    if [[ $orig != */ ]]; then
        orig="$orig/"
    fi
    if [[ $copy != */ ]]; then
        copy="$copy/"
    fi
    temp="temp/"
fi


git mv $orig $copy
git commit -m "[duplicating \`$orig\` (1/4)]"

echo "---"

SAVED=`git rev-parse HEAD`
git reset --hard HEAD^
git mv $orig $temp
git commit -m "[duplicating \`$orig\` (2/4)]"

echo "---"

# this will show:
#    CONFLICT (rename/rename): <FILE1> renamed to <pkg>/temp in HEAD and to <FILE2> in <commit-sha>.
#    Automatic merge failed; fix conflicts and then commit the result.
# this is okay.
git merge $SAVED &> /dev/null || true
git commit -a -m "[duplicating \`$orig\` (3/4)]"

echo "---"

git mv $temp $orig
git commit -m "Duplicated \`$orig\` to \`$copy\` with git line history"  # last commit gets nice msg

echo "---"

echo "ready for manual trimming!"