binsearch.py: Binary file search

#!/usr/bin/python

import sys, os, argparse
import mmap, codecs, re
import signal

if os.name != 'posix':
    exit('Platform is not supported')

# Reset SIGINT handler to default value since Python's
# handler do not respond to the signal during search
signal.signal(signal.SIGINT, signal.SIG_DFL)

def parse_args():
    p = argparse.ArgumentParser(description='Binary file search')
    p.add_argument('pattern', type=str, help='pattern to search for', metavar='PATTERN')
    p.add_argument('file', type=str, help='regular file or block device', metavar='FILE')
    p.add_argument('-r', '--regexp', action='store_true', help='do regexp search instead of fixed string')
    p.add_argument('-i', '--ignore_case', action='store_true', help='do case insensitive search (regexp)')
    p.add_argument('-p', '--print_match', action='store_true', help='print matched substring (regexp)')
    p.add_argument('-o', '--output', type=str, default='/dev/stdout', help='output file (default=stdout)')
    p.add_argument('--license', action='store_true', help='show license')
    if '--license' in sys.argv: print('Public domain') or exit(0)
    a = p.parse_args()
    a.pattern = codecs.escape_decode(a.pattern)[0]
    return a

def mmap_file(file):
    if os.stat(file).st_mode >> 12 not in (6, 8):
        exit('Only regular files and block devices are supported')
    fd = os.open(file, os.O_RDONLY)
    file_size = os.lseek(fd, 0, os.SEEK_END)
    return mmap.mmap(fd, file_size, prot=mmap.PROT_READ)

def gen_regex(a, mm):
    flags = re.DOTALL | (a.ignore_case and re.I)
    for mo in re.finditer(a.pattern, mm, flags=flags):
        yield mo.start(), mo.group(0)

def gen_fixed(a, mm):
    offset = 0
    while (offset := mm.find(a.pattern, offset+1)) >= 0:
        yield offset, None

def do_all():
    a = parse_args()
    mm = mmap_file(a.file)
    gen = gen_regex if a.regexp else gen_fixed
    f = open(a.output, 'wb')
    print_match = a.regexp and a.print_match
    exit_status = 1

    for offset,match in gen(a, mm):
        f.write(f'@ 0x{offset:010x} ({offset})\n'.encode())
        if print_match:
            f.write(match + b'\n')
        f.flush()
        exit_status = 0

    return exit_status

exit(do_all())