Gotcha: Environment variables are strings in all languages

Environment variables are always strings, causing subtle bugs when used as booleans, numbers, or compared directly.

Environment variable type pitfalls:

# Python
import os

# BAD: Truthiness check on string
DEBUG = os.environ.get('DEBUG', 'false')
if DEBUG:  # ALWAYS True! Non-empty string is truthy!
    enable_debug()

# GOOD: Explicit comparison
DEBUG = os.environ.get('DEBUG', 'false').lower() in ('true', '1', 'yes')

# BAD: Number without conversion
PORT = os.environ.get('PORT', '3000')
server.listen(PORT)  # Passing string '3000', not int 3000!

# GOOD: Convert explicitly
PORT = int(os.environ.get('PORT', '3000'))

// JavaScript / Node.js

// BAD: Falsy check
if (process.env.FEATURE_FLAG) {  // 'false' is truthy!
  enableFeature();
}

// GOOD: Explicit comparison
if (process.env.FEATURE_FLAG === 'true') {
  enableFeature();
}

// BAD: Number comparison
if (process.env.MAX_RETRIES > 3) {  // String comparison!
  // '10' > '3' is false! (string comparison: '1' < '3')
}

// GOOD: Parse first
const maxRetries = parseInt(process.env.MAX_RETRIES || '3', 10);
if (maxRetries > 3) { ... }

// BAD: undefined check with default
const timeout = process.env.TIMEOUT || 5000;
// If TIMEOUT='0', this uses 5000! ('0' is falsy)

// GOOD: Nullish coalescing
const timeout = parseInt(process.env.TIMEOUT ?? '5000', 10);

# Shell
# Empty string is falsy, any string is truthy
# Common pattern:
if [ "$DEBUG" = "true" ]; then
  set -x
fi

Environment variables have no type system. Every value is a string. Languages have different truthiness rules for strings, making implicit conversions unreliable.

Application configuration from environment