Environment variables

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  1. Environment Variables

Introduction

Environment variables are a fundamental concept in computing, particularly important when working with servers, scripting, and applications like MediaWiki. They are dynamic named values that can affect the way running processes will behave on a computer. Essentially, they provide a way to configure applications without modifying the application code itself. This article will provide a comprehensive overview of environment variables, focusing on their relevance to MediaWiki, how to set them, how to access them, and best practices for their usage. This is geared towards beginners, meaning we will avoid highly technical jargon where possible and focus on practical applications. Understanding Configuration, including environment variables, is crucial for any MediaWiki administrator.

What are Environment Variables?

Imagine you have a program that needs to know the location of a database, a specific API key, or a preferred language setting. Instead of hardcoding these values directly into the program’s source code, you can store them as environment variables.

An environment variable is a variable whose value is set outside the program, typically by the operating system or a shell (like Bash or PowerShell). The program can then *read* this value to customize its behavior.

Here's a simple analogy: Think of a recipe. The recipe lists the ingredients and instructions. An environment variable is like a note attached to the recipe saying, "If you don't have brown sugar, use maple syrup instead." The recipe doesn't change, but the outcome is adjusted based on an external factor.

Key characteristics of environment variables:

  • **Dynamic:** Their values can be changed without altering the program code.
  • **Global (to a process):** Once set, they are available to all processes spawned by the shell session or the system (depending on how they're set). A process inherits the environment variables of its parent process.
  • **String-based:** Environment variables always store values as strings. Applications must convert these strings to the appropriate data type (integer, boolean, etc.) if needed.
  • **Case Sensitivity:** On some operating systems (like Linux and macOS), environment variable names are case-sensitive. Windows, however, is generally case-insensitive. It's best practice to use consistent casing for portability.

Why Use Environment Variables?

There are several compelling reasons to utilize environment variables:

  • **Configuration Management:** Separate configuration from code. This makes your application more flexible and easier to maintain. Changing a configuration value doesn’t require a code deployment.
  • **Security:** Sensitive information like API keys, database passwords, and encryption keys should *never* be hardcoded into your application. Store them as environment variables and restrict access to the environment where they are defined. This minimizes the risk of accidental exposure. Consider using a Secrets management solution in conjunction with environment variables for increased security.
  • **Portability:** An application can run in different environments (development, testing, production) with different configurations without code changes. This is crucial for Deployment pipelines.
  • **Flexibility:** Different users or systems can have different configurations without modifying the core application.
  • **Simplified Deployment:** Environment variables make it easier to automate deployments, as you can configure the application's settings during the deployment process.
  • **Compliance:** Certain security standards and best practices mandate the use of environment variables for sensitive data.

Setting Environment Variables

The method for setting environment variables varies depending on your operating system and shell.

  • **Linux/macOS (Bash/Zsh):**
   *   **Temporary (for the current session):**
       ```bash
       export VARIABLE_NAME="value"
       ```
       This sets the variable only for the current terminal session. When you close the terminal, the variable is lost.
   *   **Persistent (across sessions):**
       Edit your shell’s configuration file (e.g., `~/.bashrc`, `~/.zshrc`). Add the `export` command to this file.  After saving, source the file:
       ```bash
       source ~/.bashrc  # or source ~/.zshrc
       ```
  • **Windows:**
   *   **Temporary (for the current session):**
       ```powershell
       $env:VARIABLE_NAME = "value"
       ```
       Or, in Command Prompt:
       ```cmd
       set VARIABLE_NAME=value
       ```
   *   **Persistent (across sessions):**
       1.  Search for "Environment Variables" in the Start Menu.
       2.  Click "Edit the system environment variables".
       3.  Click "Environment Variables...".
       4.  Under "System variables" (or "User variables" for user-specific variables), click "New...".
       5.  Enter the variable name and value, then click "OK".
  • **Docker:** Environment variables can be set in a `Dockerfile` using the `ENV` instruction or passed to a running container using the `-e` flag with `docker run`.

Accessing Environment Variables

Once set, applications can access environment variables using different methods:

  • **PHP (MediaWiki's primary language):**
   *   `getenv("VARIABLE_NAME")`: This is the most common way to access environment variables in PHP.
   *   `$_ENV["VARIABLE_NAME"]`: This is an associative array containing environment variables.  However, it's not always populated by default and may require configuration in `php.ini`.
   *   `$_SERVER["VARIABLE_NAME"]`: While primarily for server information, some environment variables are also accessible through `$_SERVER`.
  • **JavaScript (Client-side):**
   *   Accessing environment variables directly in client-side JavaScript is generally discouraged for security reasons.  Sensitive information should *never* be exposed to the client.  However, you can pass environment variables to the client during the build process (e.g., using a build tool like Webpack) and store them in a configuration file or constants.
  • **Shell Scripts:**
   *   `$VARIABLE_NAME`:  Directly access the variable's value using the dollar sign.
   *   `${VARIABLE_NAME}`:  Use curly braces to explicitly delimit the variable name, especially when it's followed by other characters.

Environment Variables in MediaWiki

MediaWiki relies heavily on configuration. While `LocalSettings.php` is the primary configuration file, environment variables provide a powerful way to override or supplement these settings.

  • **Database Credentials:** Storing database username, password, and host information as environment variables enhances security.
  • **API Keys:** If your MediaWiki instance integrates with external services (e.g., Google Analytics, CAPTCHA providers), store their API keys as environment variables.
  • **Cache Settings:** Configure cache settings (e.g., Memcached server address) using environment variables.
  • **Maintenance Mode:** Use an environment variable to easily switch MediaWiki into and out of maintenance mode.
  • **Debugging/Logging:** Control debugging levels and logging settings via environment variables.
  • **Customization:** Override default settings for various MediaWiki features using environment variables.
    • Example (LocalSettings.php):**

```php <?php // ... other settings ...

$wgDBuser = getenv('MW_DB_USER') ?: 'default_user'; $wgDBpassword = getenv('MW_DB_PASSWORD') ?: 'default_password'; $wgDBserver = getenv('MW_DB_SERVER') ?: 'localhost'; $wgDBname = getenv('MW_DB_NAME') ?: 'mediawiki';

// Enable maintenance mode if the MAINTENANCE_MODE environment variable is set to 'true' if (getenv('MAINTENANCE_MODE') === 'true') { 

   define('MW_MAINTENANCE', true);

}

// ... other settings ... ?> ```

In this example, if the environment variables `MW_DB_USER`, `MW_DB_PASSWORD`, `MW_DB_SERVER`, and `MW_DB_NAME` are not set, the default values will be used. Similarly, maintenance mode is enabled if `MAINTENANCE_MODE` is set to `true`.

Best Practices

  • **Naming Conventions:** Use consistent naming conventions for environment variables. Consider using uppercase letters and underscores (e.g., `API_KEY`, `DATABASE_URL`).
  • **Security:** Never store sensitive information directly in your code. Always use environment variables. Restrict access to the environment where these variables are defined.
  • **Documentation:** Document all environment variables used by your application. Clearly explain their purpose and expected values.
  • **Default Values:** Provide reasonable default values for environment variables in your code. This makes your application more resilient to missing configuration.
  • **Validation:** Validate the values of environment variables to ensure they are in the correct format and within acceptable ranges. This can prevent unexpected errors.
  • **Configuration Management Tools:** For complex deployments, consider using a configuration management tool (e.g., Ansible, Chef, Puppet) to manage environment variables.
  • **Avoid Hardcoding:** Resist the temptation to hardcode values in your code, even for development purposes. Use environment variables consistently.
  • **.env files:** For development, using a `.env` file with a library like `vlucas/phpdotenv` can be very helpful to manage environment variables locally without having to set them system-wide.
  • **Regular Review:** Periodically review your environment variables to ensure they are still relevant and secure.
  • **Consider containerization:** Using Docker and similar technologies allows for easy management of environment variables in isolated environments, improving consistency and security.

Common Pitfalls

  • **Case Sensitivity Issues:** Remember that environment variable names are case-sensitive on some operating systems.
  • **Missing Variables:** If an environment variable is not set, your application may behave unexpectedly. Always provide default values.
  • **Incorrect Values:** If an environment variable contains an incorrect value, your application may not function correctly. Validate the values.
  • **Security Risks:** Exposing sensitive information in environment variables that are accessible to unauthorized users can lead to security breaches.
  • **Deployment Issues:** Incorrectly configured environment variables can cause deployment failures. Thoroughly test your deployments.
  • **Conflicting Variables:** Duplicated variable names with different values can lead to unpredictable behavior.

Related Concepts and Further Reading

Technical Analysis & Trading Strategies (Related Links)

While not directly related to environment variables, these resources can be helpful for those managing and developing applications like MediaWiki that might integrate with financial data or services:

MediaWiki Configuration PHP Server Administration Security Best Practices Deployment LocalSettings.php Secrets management Docker Configuration files Bash scripting

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