Python Project Guide: Making Scripts

Python is an excellent language for system administration, easily replacing tools like bash and AWK for many tasks. This guide focuses on making useful Python 3 scripts to automate jobs, perform security checks, and handle system files. A good script breaks down a large task into smaller, manageable pieces, making it easier to debug and maintain.

💻 Reading from Standard Input and Parsing Logs

One common sysadmin task is parsing log files. A Python script can read data line-by-line from standard input (stdin), allowing you to pipe data into it just like a shell command (e.g., cat access.log | ./my_script.py).

import sys
import re

counter = dict()
for line in sys.stdin:
    # Regular expression to find the host IP address
    host = re.findall(r'(\S+)', line)[0]
    counter[host] = counter.get(host, 0) + 1

for host, count in counter.items():
    print(f"{host}: {count}")

This script uses the re module for regular expressions to parse an Apache log file and count requests per IP address.

💻 Getting System Information with `psutil`

The cross-platform psutil library is a powerful tool for retrieving information about running processes and system utilization.

1. Installation:
   pip install psutil
2. Example Usage:

   import psutil
   
   # Get CPU usage over 1 second
   print(f"CPU Usage: {psutil.cpu_percent(interval=1)}%")
   
   # Get virtual memory stats
   print(psutil.virtual_memory())
   
   # Get info for a specific process (PID 1 is usually 'init')
   p = psutil.Process(1)
   print(p.name(), p.uids())

💻 Walking File Systems with `os.walk`

Another essential task is working with files and directories. The os.walk() function is perfect for recursively traversing a directory tree.

import os

directory = '.'
for root, dirs, files in os.walk(directory):
    for file in files:
        pathname = os.path.join(root, file)
        file_size = os.path.getsize(pathname)
        print(f"{pathname} - {file_size} bytes")

This script walks through the current directory and all its subdirectories, printing the full path and size of every file it finds.

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💻 Continue Your Learning Journey

• Python Project Guide: How to Get Started with Python 3
• Python Project Guide: Using Functions in Python 3
• Python Project Guide: Build an FTP Client & Server
• Python Project Guide: Times, Dates & Numbers
• Python Project Guide: NumPy & SciPy: For Science!

More Topics

• Python Project Guide: NumPy & SciPy: For Science!
• Python Project Guide: Times, Dates & Numbers
• Python Project Guide: Build an FTP Client & Server
• Python Project Guide: Using Functions in Python 3
• Python Project Guide: How to Get Started with Python 3
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