#!/usr/bin/python3

import base64
import sys
import subprocess

def shell_safe(cmd):
    """shell_safe(cmd): return a string that can be passed to 
         set -- <string>
       to produce the same array that cmd represents.
       
    internally we utilize 'getopt's ability/knowledge on how to quote
    strings to be safe for shell.  This implementation could be changed
    to be pure python.  It is just a matter of correctly escaping 
    or quoting characters like: ' " ^ & $ ; ( ) ... """
    out = subprocess.check_output(
        ["getopt", "--shell", "sh", "--options", "", "--", "--"] + list(cmd))
    # out contains ' -- <data>\n'. drop the ' -- ' and the '\n'
    return out[4:-1].decode()

def shell_pack(cmd):
    """shell_pack(cmd): return a string that can shuffled through 'sh'
       and will execute cmd.
       
       in python subprocess terms:
           check_output(cmd) == check_output(shell_pack(cmd), shell=True)"""

    if isinstance(cmd, str):
        cmd = [cmd]
    else:
        cmd = list(cmd)

    stuffed = shell_safe(cmd)
    # for whatever reason b64encode returns bytes when it is clearly
    # representable as a string by nature of being base64 encoded.
    b64 = base64.b64encode(stuffed.encode()).decode()
    return 'eval set -- "$(echo %s | base64 --decode)" && exec "$@"' % b64


args = sys.argv[1:]
shell_packed = shell_pack(args)
print("input: %s" % args)
print("shellpack: %s" % shell_packed)
print("output: %s" % subprocess.check_output(shell_packed, shell=True))