Get IP address from last line of log file using Regex

Question

I am trying to use Python Regex to get the IP address from the last line of a log.

I can get an IP if I search through the entire log. For example:

with open("read.log", "r+") as log:
    for line in log:
        address = "^\d{1,3}.\d{1,3}.\d{1,3}.\d{1,3}$"
        match = re.match(address, line)

But when I try to just read the last line and get an IP address, I do not get any results. How do I fix this?

import re

def run():

    try:
        logfile = open('read.log', 'r')
#       print ('First line in log: ',logfile.readline())

        for line in logfile:  
            x = line
            for ip in x:
                address = "^\d{1,3}.\d{1,3}.\d{1,3}.\d{1,3}$"
                match = re.match(address, ip)
                logfile.close   
        print ('Last Line: ', match)


    except OSError as e:
        print (e)

run()

My read.log looks like this...

10.1.177.198 Tue Jun 19 09:25:16 CDT 2018
10.1.160.198 Tue Jun 19 09:25:38 CDT 2018
10.1.177.198 Tue Jun 19 09:25:36 CDT 2018
10.1.177.198 Tue Jun 19 09:26:38 CDT 2018
10.1.177.198 Tue Jun 19 09:27:16 CDT 2018
10.1.177.198 Tue Jun 19 09:28:38 CDT 2018

@Barmar Iterate in characters of lines is not necessary for you to do, which re.match has already done for you. — Geno Chen
– Geno Chen, Commented Jun 19, 2018 at 17:00
Is the IP always the first field? Just use ip = line.split()[0] — Barmar
– Barmar, Commented Jun 19, 2018 at 17:00

Demian Brecht · Accepted Answer · 2018-06-19 17:08:39Z

1

The problem is your regex. ^ matches the beginning of a line, $ the end. If your log lines /only/ had the IP address, your code would work.

>>> import re
>>> m = re.compile("^\d{1,3}.\d{1,3}.\d{1,3}.\d{1,3}$")
>>> m.search('123.123.123.123')
<_sre.SRE_Match object; span=(0, 15), match='123.123.123.123'>

However, that's not the case. The following change will fix your search issue:

>>> import re
>>> m = re.compile("(^\d{1,3}.\d{1,3}.\d{1,3}.\d{1,3})\s")
>>> m.search('10.1.177.198 Tue Jun 19 09:28:38 CDT 2018').groups()[0]
>>> '10.1.177.198'

answered Jun 19, 2018 at 17:08

Demian Brecht

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