Simple python code for overlaying a source directory on top of another (existing) dir.

overlay-dir.py

# A Python function for overlaying a source directory on top of a destination dir

import os
import shutil

def overlay_dir(prefix, src, dest):
    abs_src = os.path.abspath(src)
    abs_dest = os.path.join(prefix, dest)

    for root, dirs, files in os.walk(abs_src):
        dest_root=root.replace(abs_src, abs_dest)
        if not os.path.exists(dest_root):
            os.mkdir(dest_root)
        for f in files:
            src_file=os.path.join(root, f)
            dest_file=os.path.join(dest_root, f)
            shutil.copy2(src_file, dest_file)

if __name__ == "__main__":
    prefix = "/tmp"
    user_input = ("..", "tmp")
    overlay_dir(prefix, *user_input)