sha256.py

#!/usr/bin/env python
# file: sha256.py
# vim:fileencoding=utf-8:ft=python
#
# Copyright © 2014-2016 R.F. Smith <rsmith@xs4all.nl>.
# SPDX-License-Identifier: MIT
# Created: 2014-12-28T13:36:38+0100
# Last modified: 2020-12-16T00:26:05+0100
"""
Calculate the SHA256 checksum of files.

Meant for systems that don't come with such a utility.
"""

from hashlib import sha256
from os.path import isfile
import sys
import argparse

__version__ = "2020.12.16"

# Process the command-line arguments.
parser = argparse.ArgumentParser(description=__doc__)
hs = """compare file to this sha256 string;
        will add "[ OK ]" or "[ Failed ]" after the checksum"""
parser.add_argument("-c", "--checksum", default=None, help=hs)
parser.add_argument("-v", "--version", action="version", version=__version__)
parser.add_argument("file", nargs="*")
args = parser.parse_args(sys.argv[1:])
if not args.file:
    parser.print_help()
    exit(0)

# Process files.
if args.checksum and len(args.checksum) != 64:
    print("Invalid checksum length. Skipping comparison.")
    args.checksum = None
for nm in args.file:
    if not isfile(nm):
        continue
    with open(nm, "rb") as f:
        data = f.read()
    hexdat = sha256(data).hexdigest()
    print(f"SHA256 ({nm}) = {hexdat}", end="")
    if args.checksum:
        if args.checksum != hexdat:
            print(" [ Failed ]", end="")
        else:
            print(" [ OK ]", end="")
    print()