#!/usr/bin/env python3

import argparse
import os
import shutil
import sys

ap = argparse.ArgumentParser()
ap.add_argument("source")
ap.add_argument("destination")
ap.add_argument("--mode", "-m", type=lambda x: int(x, base=8))

args = ap.parse_args()

with open(args.source) as inf:
    tmp_dest = args.destination + "." + str(os.getpid())
    with open(tmp_dest, "w") as outf:
        first_line = inf.readline()
        if first_line.startswith("#!"):
            print("#!", sys.executable, file=outf)
        else:
            print("#!", sys.executable, file=outf)
            outf.write(first_line)
        for line in inf:
            outf.write(line)
    if args.mode is not None:
        os.chmod(tmp_dest, args.mode)
    else:
        shutil.copymode(args.source, tmp_dest)
    os.rename(tmp_dest, args.destination)