Scenario

A file contains a list of URLs that need to be processed. You need to extract the domain names (including subdomains) from these URLs for analysis.

Task

Write a Python script at /home/interview/extract_domains.py that reads URLs from /home/interview/urls.txt, extracts the domain names using regex, and saves them to /home/interview/domains.txt (one domain per line).

Example

Input URL examples:

https://www.example.com/path/to/page
http://api.service.org:8080/endpoint
ftp://files.company.co.uk/downloads

Expected output format in /home/interview/domains.txt:

www.example.com
api.service.org
files.company.co.uk

Step 1: Examine the input file

head -20 /home/interview/urls.txt

Review the URL formats to understand the patterns that need to be matched.

Step 2: Create the Python script

nano /home/interview/extract_domains.py

Write a script that uses regex to extract domains:

import re

# Read URLs from file
with open('/home/interview/urls.txt', 'r') as f:
    urls = f.readlines()

# Extract domains using regex
domains = []
pattern = r'[a-zA-Z]+://([^/:]+)'

for url in urls:
    url = url.strip()
    match = re.search(pattern, url)
    if match:
        domain = match.group(1)
        domains.append(domain)

# Write domains to output file
with open('/home/interview/domains.txt', 'w') as f:
    for domain in domains:
        f.write(domain + '\n')

print(f"Extracted {len(domains)} domains")

The regex pattern [a-zA-Z]+://([^/:]+) matches the protocol, then captures everything after :// until it hits / or : (port), extracting the full domain including subdomains.

Step 3: Run the script

python3 /home/interview/extract_domains.py

Step 4: Verify the output

head -20 /home/interview/domains.txt