Convert dmesg time offsets to real time

timesg.py

#!/usr/bin/env python3

USAGE = """ ./timesg.py TIMESTAMP [HOURS] <dmesg >dmesg-with-time """

import sys
import re
import datetime

RE = re.compile(r'^\[\s*(\d+\.\d+)\]')

def main(starttime, hours=0., *_):
    starttime = starttime + hours * 3600
    for line in sys.stdin:
        parts = RE.split(line)
        if len(parts) != 3:
            print(line, end='')
            continue
        _, t_off, tail = parts
        t_off = float(t_off)
        time = datetime.datetime.fromtimestamp(starttime + t_off)
        print('[' + time.strftime('%Y-%m-%d %H:%M:%S') + ']' + tail, end='')

if __name__ == '__main__':
    if len(sys.argv) > 1:
        main(*map(float, sys.argv[1:]))
    else:
        print(USAGE)