Safely Source Environment Variables from a .env File

#!/bin/bash

# Script to demonstrate sourcing environment variables from a .env file

# Default .env file path. Can be overridden.
ENV_FILE=".env"

# Function to load environment variables from a .env file
load_env() {
  local env_path="$1"
  if [ -z "$env_path" ]; then
    env_path="$ENV_FILE"
  fi

  if [ ! -f "$env_path" ]; then
    echo "Error: .env file not found at $env_path" >&2
    return 1
  fi

  echo "Loading environment variables from $env_path..."
  while IFS='=' read -r key value; do
    # Skip comments and empty lines
    if [[ -z "$key" || "$key" =~ ^# ]]; then
      continue
    fi

    # Remove leading/trailing whitespace from key and value
    key=$(echo "$key" | xargs)
    value=$(echo "$value" | xargs)

    # Remove quotes from value (single or double) if they exist
    if [[ "$value" =~ ^["'].*["']$ ]]; then
      value="${value:1:-1}"
    fi

    # Export the variable into the current shell's environment
    export "$key"="$value"
    echo "  Loaded: $key"
  done < "$env_path"
  echo "Environment variables loaded."
  return 0
}

# Create a dummy .env file for demonstration
cat > "$ENV_FILE" << EOF
# This is a comment

DATABASE_HOST=localhost
DATABASE_PORT=5432
API_KEY="your_api_key_123"
SECRET_PHRASE='a long phrase with spaces'
APP_ENV=development

EOF

# --- Main Script Logic ---

if load_env "$ENV_FILE"; then
  echo "
Accessing loaded variables:"
  echo "DATABASE_HOST: $DATABASE_HOST"
  echo "DATABASE_PORT: $DATABASE_PORT"
  echo "API_KEY: $API_KEY"
  echo "SECRET_PHRASE: $SECRET_PHRASE"
  echo "APP_ENV: $APP_ENV"
  echo "
Attempting to access a non-existent variable (will be empty):"
  echo "NON_EXISTENT_VAR: $NON_EXISTENT_VAR"
else
  echo "Failed to load environment variables. Exiting." >&2
  exit 1
fi

# Cleanup dummy .env file
rm "$ENV_FILE"