05-cli-tools-argparse

Building CLI Tools with argparse

kubectl, terraform, aws, helm — a lot of the DevOps world runs on CLIs. This module turns the log analyzer into a real command-line tool using Python's built-in argparse.

Files

• app.log — sample log
• log_analyzer_cli.py — the CLI tool

python log_analyzer_cli.py --file app.log
python log_analyzer_cli.py --file app.log --out summary.json
python log_analyzer_cli.py --file app.log --level ERROR
python log_analyzer_cli.py --help

If the file is missing it prints a friendly error and exits with code 2:

$ python log_analyzer_cli.py --file nope.log
Error: log file not found: nope.log

Practice

Build the CLI yourself:

1. Required --file argument.
2. Optional --out (output JSON path) and --level (INFO/WARNING/ERROR).
3. If --file doesn't exist, print an error and sys.exit(2).
4. Count the levels and print the summary (or just --level if given).
5. If --out is set, write the counts as JSON.