Python实现tail命令（功能暂时比较简陋）

tail.py

#!/usr/bin/env python3
# coding: utf-8

__author__ = "ChenyangGao <https://chenyanggao.github.io/>"
__version__ = (0, 0, 1)
__all__ = ["tail"]

from sys import stdout
from time import sleep


CHUNK_SIZE = 1024


def tail(path, nlines=10, sleep_interval=1.0, file=stdout, encoding=None):
    """Print the last lines of a file.

    :param path: The path of the file to be opened or an integer file descriptor of the file to be wrapped.
    :param nlines: Output the last `nlines` (default 10) lines.
    :param sleep_interval: Sleep for approximately `sleep_interval` seconds (default 1.0) between iterations.
    :param file: The file object to be written into.
    :param encoding: `encoding` is the name of the encoding used to decode or encode the file.
    """
    nlines += 1
    write, flush = file.write, file.flush
    with open(path, encoding=encoding) as f:
        encoding = f.encoding
        readline = f.readline
        file_buffer = f.buffer
        last_pos = f.seek(0, 2)
        if last_pos:
            last_lines = [b""]
            i = last_pos
            while i >= CHUNK_SIZE:
                i = file_buffer.seek(-CHUNK_SIZE, 1)
                ls = file_buffer.read(CHUNK_SIZE).split(b"\n")
                last_lines[-1] = ls[-1] + last_lines[-1]
                last_lines.extend(reversed(ls[:-1]))
                if len(last_lines) > nlines:
                    break
                file_buffer.seek(-CHUNK_SIZE, 1)
            else:
                file_buffer.seek(0, 0)
                ls = file_buffer.read(i).split(b"\n")
                last_lines[-1] = ls[-1] + last_lines[-1]
                last_lines.extend(reversed(ls[:-1]))
            write(b"\n".join(reversed(last_lines[:nlines])).decode(encoding))
            flush()
            f.seek(last_pos, 0)
        while True:
            line = readline()
            if not line:
                sleep(sleep_interval)
            write(line)
            flush()


if __name__ == "__main__":
    from argparse import ArgumentParser

    parser = ArgumentParser(description="Print the last lines of a file")
    parser.add_argument("path", help="The path of the file to be opened")
    parser.add_argument("-n", "--nlines", metavar="NUM", default=10, type=int, help="Output the last NUM (default 10) lines")
    parser.add_argument("-s", "--sleep_interval", metavar="N", default=1.0, type=float, help="Sleep for approximately N seconds (default 1.0) between iterations")
    parser.add_argument("-e", "--encoding", help="The name of the encoding used to decode or encode the file.")

    args = parser.parse_args()
    try:
        tail(args.path, nlines=args.nlines, sleep_interval=args.sleep_interval, encoding=args.encoding)
    except KeyboardInterrupt:
        pass