We are almost at the end of the chapter. In this last section, let's make the Paramiko program more reusable. There is one downside of our existing script: we need to open up the script every time we want to add or delete a host, or whenever we need to change the commands we want to execute on the remote host. This is due to the fact that both the host and command information are statically entered inside of the script. Hardcoding the host and command has a higher chance of making mistakes. Besides, if you were to pass on the script to colleagues, they might not feel comfortable working in Python, Paramiko, or Linux.

By making both the host and command files be read in as parameters for the script, we can eliminate some of these concerns. Users (and a future you) can simply modify these text files when you need to make host or command changes.

We have incorporated the change in the script named chapter5_4.py.

Instead of hardcoding the commands, we broke the commands into a separate commands.txt file. Up to this point, we have been using show commands; in this example, we will make configuration changes. In particular, we will change the logging buffer size to 30000 bytes:

$ cat commands.txt
config t
logging buffered 30000
end
copy run start

The device's information is written into a devices.json file. We choose JSON format for the device's information because JSON data types can be easily translated into Python dictionary data types:

$ cat devices.json
{
     "iosv-1": {"ip": "172.16.1.20"},
     "iosv-2": {"ip": "172.16.1.21"}
}

In the script, we made the following changes:

  with open('devices.json', 'r') as f:
      devices = json.load(f)

  with open('commands.txt', 'r') as f:
      commands = [line for line in f.readlines()]

Here is an abbreviated output from the script execution:

$ python3 chapter5_4.py
Username: cisco
Password:
b'terminal length 0rniosv-2#config trnEnter configuration commands, one per line. End with CNTL/Z.rniosv-2(config)#'
b'logging buffered 30000rniosv-2(config)#'
...

Do a quick check to make sure the change has taken place in both running-config and startup-config:

iosv-1#sh run | i logging
logging buffered 30000
iosv-1#sh start | i logging
logging buffered 30000
iosv-2#sh run | i logging
logging buffered 30000
iosv-2#sh start | i logging
logging buffered 30000