Extract specific string from Telnet output with Python

Question

I'm trying to write a Python script to telnet to a bunch of Cisco routers, extract the running configuration and save it. Each router has a different name so what I would like to do is to extract the device name and save the output file with that name. For example this a snippet of a Cisco router output where there is a line "hostname ESW1":

Current configuration : 1543 bytes

!
version 12.4
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname ESW1
!
boot-start-marker
boot-end-marker
!

I'm using telnetlib and I can get the output and save it in a variable. My question is how can I identify that specific line and extract the "ESW1" string after the "hostname "?

Answer 1

Use a regular expression:

config_string = '''Current configuration : 1543 bytes

!
version 12.4
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname ESW1
!
boot-start-marker
boot-end-marker
!'''

import re
hostname = re.findall(r'hostname\s+(\S*)', config_string)[0]
print hostname
# ESW1

Or, if you don't like regular expressions:

for line in config_string.splitlines():
    if line.startswith('hostname'):
    hostname = line.split()[1]
print hostname
# ESW1

I think that the regex will run faster than the loop.