Netmiko, ConnectHandler, send_command & credentials from the environment

Run a command on a switch

Lesson 1 of 20 · 12 min · Module 1: First steps with automation

Network automation starts small: log in to a switch from Python, run a show command and read the answer. The Netmiko library does the SSH part for you, on Cisco, Huawei and many other vendors.

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Free. No installation: you write and run the code in your browser, and it is checked automatically.

By the end, you’ll be able to…

Describe a device with a Netmiko dictionary
Run a show command and keep its output
Keep credentials out of your code

The idea

Netmiko describes a device with a dictionary: device_type picks the driver (cisco_ios for Cisco IOS, huawei for Huawei VRP), then host, username and password. ConnectHandler(**device) logs in and returns a connection, and send_command() returns everything the device printed as one string. A with block closes the session for you. Passwords never go in the code: read them from environment variables with os.environ.

Every exercise in this course runs against a practice network inside your browser: a core switch and access switches in Bucharest and Cluj, running simulated Cisco IOS and Huawei VRP. Nothing you send reaches a real device, so experiment freely. The code you write here works with the real Netmiko after pip install netmiko.

import os
from netmiko import ConnectHandler

device = {
    "device_type": "cisco_ios",
    "host": "10.0.0.11",
    "username": os.environ["NET_USERNAME"],
    "password": os.environ["NET_PASSWORD"],
}
with ConnectHandler(**device) as conn:
    print(conn.find_prompt())

01Credentials come from the environment

The practice lab sets NET_USERNAME and NET_PASSWORD for you, the way a CI job or a vault would on a real team. os.environ reads them like a dictionary.

import os

print(os.environ["NET_USERNAME"])
print("NET_PASSWORD" in os.environ)

Output

netadmin
True

02Log in and look at the prompt

ConnectHandler(**device) unpacks the dictionary into keyword arguments and logs in. find_prompt() returns the prompt; # means privileged mode on Cisco.

from netmiko import ConnectHandler

device = {
    "device_type": "cisco_ios",
    "host": "10.0.0.11",
    "username": os.environ["NET_USERNAME"],
    "password": os.environ["NET_PASSWORD"],
}
with ConnectHandler(**device) as conn:
    print(conn.find_prompt())

Output

sw1#

03A show command returns text

send_command() waits for the prompt to come back and returns what the device printed, without the command and the prompt. It is a plain string: printing it shows the table, and Python can search or split it.

with ConnectHandler(**device) as conn:
    clock = conn.send_command("show clock")
print(type(clock).__name__)
print(clock)

Output

str
09:00:05.785 UTC Mon Oct 19 2026

Your turn

Connect to the core switch core1 at 10.0.0.1 (Cisco IOS). Store the output of show ip interface brief in a variable named output and print it. Read the username and password from the NET_USERNAME and NET_PASSWORD environment variables.

What the checks look for

output holds the interfaces of core1
The output is printed
Logged in to core1
The password is not written in the code

Try it in the editor →

Take this with you

ConnectHandler(**device) logs in; send_command() returns the output as one string.

Go a little further

Also print conn.find_prompt() and only the first line of show version (output.splitlines()[0]).

By the end, you’ll be able to…

The idea

01Credentials come from the environment

02Log in and look at the prompt

03A show command returns text

Your turn

What the checks look for

Take this with you

Go a little further

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