fifo_size.py

# Print the number of bytes unread in a fifo.
# David Coles <coles.david@gmail.com>

import argparse
import ctypes
import fcntl
import os
import sys
import termios

if __name__ == "__main__":
    parser = argparse.ArgumentParser()
    parser.add_argument("path")
    args = parser.parse_args()

    fd = os.open(args.path, os.O_RDONLY|os.O_NONBLOCK)
    size = ctypes.c_int(0)
    fcntl.ioctl(fd, termios.FIONREAD, size, True)

    print(size.value)