filecut is a tool to extract a chunk of bytes within a binary file

filecut.py

#!/usr/bin/env python3

import sys
import os


def main(infile, extent):
    try:
        begin, end = extent.split("-")
        size = end - begin
    except ValueError:
        # Just like GDB expression
        begin, size = extent.split("@")

    begin = int(begin, base=0)
    size = int(size, base=0)

    with open(infile, "rb") as f:
        f.seek(begin)
        sys.stdout.buffer.write(f.read(size))


if __name__ == "__main__":
    main(sys.argv[1], sys.argv[2])