python3实现tailf命令的示例代码

import re
import time

import os
import argparse


def follow(thefile):
    thefile.seek(0, os.SEEK_END)
    while True:
        _line = thefile.readline()
        if not _line:
            time.sleep(0.1)
            continue
        yield _line


class Pipe(object):
    def handle(self, _line):
        pass


class AwkPipe(Pipe):
    def __init__(self, fs, script):
        self.fs = fs
        self.script = script

    def handle(self, _line: str):
        clos = _line.split(self.fs)
        try:
            return self.script.format(*clos)
        except IndexError as e:
            return "parse_err:" + self.script + str(clos)


class GrepPipe(Pipe):
    def __init__(self, grep_str):
        self.grep_str = grep_str

    def handle(self, _line):
        if re.search(grep, _line):
            return _line
        return None


class PrintPipe(Pipe):
    def handle(self, _line):
        if _line.endswith("\n"):
            print(_line, end="")
        else:
            print(_line)


if __name__ == '__main__':
    arg_parser = argparse.ArgumentParser()
    arg_parser.add_argument("file")
    arg_parser.add_argument("-F", help="分隔符", required=False)
    arg_parser.add_argument("-s", help="脚本，使用format的{0}格式，{0}标识分割后的第一个元素占位，依次递增。",
                            required=False)
    arg_parser.add_argument("-g", "--grep", help="过滤字符，支持正则", required=False)
    args = arg_parser.parse_args()
    logfile = open(args.file, "r", encoding='utf-8')
    grep = args.grep
    pipes = []
    if args.F and args.s:
        pipes.append(AwkPipe(args.F, args.s))
    if grep:
        pipes.append(GrepPipe(grep))
    pipes.append(PrintPipe())
    try:
        loglines = follow(logfile)
        for line in loglines:
            _tmp_line = line.strip()
            if not _tmp_line:
                continue
            for pipe in pipes:
                _tmp_line = pipe.handle(_tmp_line)
                if _tmp_line is None:
                    break
    except KeyboardInterrupt:
        pass

#!/usr/bin/env python
#!encoding:utf-8
'''
Python-Tail - Unix tail follow implementation in Python.

python-tail can be used to monitor changes to a file.

Example:
    import tail

    # Create a tail instance
    t = tail.Tail('file-to-be-followed')

    # Register a callback function to be called when a new line is found in the followed file.
    # If no callback function is registerd, new lines would be printed to standard out.
    t.register_callback(callback_function)

    # Follow the file with 5 seconds as sleep time between iterations.
    # If sleep time is not provided 1 second is used as the default time.
    t.follow(s=5) '''

# Author - Kasun Herath <kasunh01 at gmail.com>
# Source - https://github.com/kasun/python-tail

import os
import sys
import time

class Tail(object):
    ''' Represents a tail command. '''
    def __init__(self, tailed_file):
        ''' Initiate a Tail instance.
            Check for file validity, assigns callback function to standard out.

            Arguments:
                tailed_file - File to be followed. '''
        self.check_file_validity(tailed_file)
        self.tailed_file = tailed_file
        self.callback = sys.stdout.write

    def follow(self, s=1):
        ''' Do a tail follow. If a callback function is registered it is called with every new line.
        Else printed to standard out.

        Arguments:
            s - Number of seconds to wait between each iteration; Defaults to 1. '''

        with open(self.tailed_file) as file_:
            # Go to the end of file
            file_.seek(0,2)
            while True:
                curr_position = file_.tell()
                line = file_.readline()
                if not line:
                    file_.seek(curr_position)
                else:
                    self.callback(line)
                time.sleep(s)

    def register_callback(self, func):
        ''' Overrides default callback function to provided function. '''
        self.callback = func

    def check_file_validity(self, file_):
        ''' Check whether the a given file exists, readable and is a file '''
        if not os.access(file_, os.F_OK):
            raise TailError("File '%s' does not exist" % (file_))
        if not os.access(file_, os.R_OK):
            raise TailError("File '%s' not readable" % (file_))
        if os.path.isdir(file_):
            raise TailError("File '%s' is a directory" % (file_))

class TailError(Exception):
    def __init__(self, msg):
        self.message = msg
    def __str__(self):
        return self.message
        
if __name__=='__main__':
    args = sys.argv
    if len(args)<2:
        print 'need one filename parameter'
        exit(1)
    t = Tail(args[1])
    #t.register_callback(print_line)
    t.follow()