Windows log file watcher

logtailer.py

"""Tailer"""

import time
import argparse
import sys
import os


def tail(filename: str, codes: list[int] = None, *, n: int = 1):
    with open(filename, "r") as fp:
        lines = fp.readlines()[-(n+1):-1]
        for line in lines:
            if codes is not None:            
                if int(line.split()[-2].strip()) in codes:
                    print(line, end="")
            else:
                print(line, end="")
        print()
        
def follow(filename, codes: list[int] = None):
    with open(filename, "r") as fp:
        while True:
            try:
                where = fp.tell()
                line = fp.readline()
                if not line:
                    time.sleep(1)
                    fp.seek(where)
                else:
                    if codes is not None:
                        if int(line.split()[-2].strip()) in codes:
                            print(line, end="")
                    else:
                        print(line, end="")
            except KeyboardInterrupt:
                sys.exit()
                
if __name__ == "__main__":
    parser = argparse.ArgumentParser(
        prog="IIS log viewer",
        description="View a IIS log and watch for changes",
    )
    parser.add_argument("-f", "--log-file", action="store", help="Full windows path to logfile")
    parser.add_argument("-n", "--lines", action="store", default=1, type=int)
    parser.add_argument("-c", "--codes", default=None, type=int, nargs="+")
    parser.add_argument("-a", "--action", default="tail", const="tail", nargs="?",
                       choices=["tail", "follow"],
                       help="tail the file n-lines or follow the file interactively", )
    args = parser.parse_args()
    if not args.log_file:
        parser.print_help()
        sys.exit()
    if args.action == "tail":
        tail(args.log_file, codes=args.codes, n=int(args.lines))
    elif args.action == "follow":
        follow(args.log_file, codes=args.codes)