Shebang proxy, specifically for Windows

shebang.py

#!/usr/bin/env python

import os, sys
import subprocess, shutil, shlex
from pathlib import Path

def getShebangLine(executable_path):
	with open(executable_path, "rb") as f:
		magic = f.read(2)
		if magic != b"#!":
			return None

		shebang = f.readline()
		return shebang.decode("utf8").strip()

def getPathext(additions):
	parsed_pathext = (os.environ.get("PATHEXT") or "").split(os.pathsep)
	return_value = parsed_pathext + additions
	os.environ["PATHEXT"] = f"{os.pathsep}".join(return_value)
	return return_value

def findCorrectExtension(parsed_pathext, extensionless_filepath):
	for possible_extension in parsed_pathext:
		potential_fullpath = Path(extensionless_filepath).with_suffix(possible_extension)
		if potential_fullpath.is_file():
			return potential_fullpath

	return extensionless_filepath

if __name__ == "__main__":
	import argparse

	parser = argparse.ArgumentParser(description="Parse an execute a shebang line from a script")
	parser.add_argument("script_file", type=Path)
	parser.add_argument("arguments", type=str, nargs="*")
	args = parser.parse_args()

	env_pathext = getPathext([".PS1", ".SH"])
	executable_path = args.script_file

	if str(executable_path) == executable_path.name: #relative paths passed to else
		absolute_executable_path = Path(shutil.which(executable_path.name) or executable_path.name)
	else:
		absolute_executable_path = (executable_path if executable_path.suffix else findCorrectExtension(env_pathext, executable_path)).resolve()

	if not absolute_executable_path.is_file():
		print(f"Can't find \"{executable_path}\"", file=sys.stderr)
		sys.exit(1)

	if not os.access(absolute_executable_path, os.X_OK):
		print(f"\"{absolute_executable_path}\" is not executable", file=sys.stderr)
		sys.exit(1)

	shebang = getShebangLine(absolute_executable_path)
	if shebang == None:
		print(f"\"{absolute_executable_path}\" does not have a shebang line", file=sys.stderr)
		sys.exit(1)

	parsed_shebang = shlex.split(shebang)
	if os.name == "nt" and parsed_shebang[0] == "/usr/bin/env":
		parsed_shebang[0] = "env"
	subprocess.run(parsed_shebang + [absolute_executable_path] + args.arguments)