Isolate differences between two directories into a new directory

cpdiff.sh

#!/usr/bin/env bash

# Copy difference only
#
# @param 1 - input path to base version
# @param 2 - input path to extended version
# @param 3 - output path of diff-only version
cpdiff()
{
	(( $# < 3 )) && {
		grep '^#[^!]' $0
		return 1
	}

	[ -d "$3" ] && {
		echo "$3 already exists" >&2
		return 1
	}

	diff -rq $1 $2 |
		#          Files A  and  B    differ
		#          Only  in DIR: FILE
		while read TYPE  X  DIR  FILE X
	do
		case "$TYPE" in
			Files*)
				DST="$3/${FILE#*/}"
				DST="${DST%/*}"

				mkdir -p "$DST" &&
					cp "$FILE" "$DST/"
				;;
			Only*)
				SRC=${DIR%:}
				DST="$3/${SRC#*/}"
				SRC="$SRC/$FILE"

				mkdir -p "$DST" &&
					cp -r "$SRC" "$DST/"
				;;
			*)
				echo "warning: cannot process line \"$TYPE...\"" >&2
		esac
	done
}

if [ "$BASH_SOURCE" == "$0" ]
then
	cpdiff "$@"
fi