Gotcha: Environment variables are always strings

Environment variables are always strings but code treats them as booleans or numbers, leading to subtle bugs.

Always explicitly convert environment variables:

# Python:
import os

# BAD - truthy string:
DEBUG = os.getenv('DEBUG') # 'false' is truthy in Python!
if DEBUG: # True! 'false' is a non-empty string

# GOOD:
DEBUG = os.getenv('DEBUG', 'false').lower() in ('true', '1', 'yes')
PORT = int(os.getenv('PORT', '3000'))
TIMEOUT = float(os.getenv('TIMEOUT', '30.0'))

// JavaScript/Node.js:
// BAD:
const debug = process.env.DEBUG; // 'false' is truthy!
if (debug) { ... } // Always true if set!

// GOOD:
const debug = process.env.DEBUG === 'true';
const port = parseInt(process.env.PORT || '3000', 10);
const ratio = parseFloat(process.env.RATIO || '0.5');

// Common trap with PORT:
process.env.PORT = '3000';
if (process.env.PORT === 3000) { } // FALSE! String !== Number
if (process.env.PORT == 3000) { } // true (loose equality)

// Docker-compose gotcha:
// environment:
// DEBUG: false # YAML boolean -> Docker sets as empty string!
// DEBUG: 'false' # String 'false' -> correct