Environment variables could be useful for handling application **settings**, as part of the **installation** of Python, etc.

## Create and Use Env Vars { #create-and-use-env-vars }

You can **create** and use environment variables in the **shell (terminal)**, without needing Python:

 */
package org.codelibs.fess.exception;

/**
 * System exception class for the Fess search engine.
 * This exception is thrown when system-level errors occur in the Fess application,
 * such as configuration errors, initialization failures, or critical runtime issues.
 */
public class FessSystemException extends RuntimeException {

    /** Serial version UID for serialization compatibility */

worker_processes  auto;

error_log  /var/log/nginx/error.log warn;
pid        /var/run/nginx.pid;

events {
    worker_connections  4096;
}

http {
    include       /etc/nginx/mime.types;
    default_type  application/octet-stream;

    log_format  main  '$remote_addr - $remote_user [$time_local] "$request" '
                      '$status $body_bytes_sent "$http_referer" '
                      '"$http_user_agent" "$http_x_forwarded_for"';

            .url("https://api.github.com/repos/square/okhttp/issues")
            .header("User-Agent", "OkHttp Headers.java")
            .addHeader("Accept", "application/json; q=0.5")
            .addHeader("Accept", "application/vnd.github.v3+json")
            .build()

        client.newCall(request).execute().use { response ->
          if (!response.isSuccessful) throw IOException("Unexpected code $response")

import okhttp3.WebSocketListener;
import okio.ByteString;

/**
 * API access to the <a href="https://api.slack.com/apps">Slack API</a> as an application. One
 * instance of this class may operate without a user, or on behalf of many users. Use the Slack API
 * dashboard to create a client ID and secret for this application.
 *
 * <p>You must configure your Slack API OAuth and Permissions page with a localhost URL like {@code

 */
internal data class DerHeader(
  /**
   * Namespace of the tag.
   *
   * This value is encoded in bits 7 and 8 of the first byte of each value.
   *
   * ```
   * 0b00xxxxxx Universal
   * 0b01xxxxxx Application
   * 0b10xxxxxx Context-Specific
   * 0b11xxxxxx Private
   * ```
   */
  var tagClass: Int,
  /** Identifies which member in the ASN.1 schema the field holds. */
  var tag: Long,
  /**

  @SuppressLint("NewApi")
  override fun getSelectedProtocol(sslSocket: SSLSocket): String? =
    try {
      // SSLSocket.getApplicationProtocol returns "" if application protocols values will not
      // be used. Observed if you didn't specify SSLParameters.setApplicationProtocols
      when (val protocol = sslSocket.applicationProtocol) {
        null, "" -> null
        else -> protocol

     <span style="background-color:#007166"><font color="#D3D7CF"> INFO </font></span>  Waiting for application startup.
     <span style="background-color:#007166"><font color="#D3D7CF"> INFO </font></span>  Application startup complete.
```

</div>

In the output, there's a line with something like:

```hl_lines="4"

<span style="color: green;">INFO</span>:     Started server process [28722]
<span style="color: green;">INFO</span>:     Waiting for application startup.
<span style="color: green;">INFO</span>:     Application startup complete.
```

</div>

/// note

📋 `uvicorn main:app` 🔗:

* `main`: 📁 `main.py` (🐍 "🕹").
* `app`: 🎚 ✍ 🔘 `main.py` ⏮️ ⏸ `app = FastAPI()`.

  /**
   * Returns an exception handler that exits the system. This is particularly useful for the main
   * thread, which may start up other, non-daemon threads, but fail to fully initialize the
   * application successfully.
   *
   * <p>Example usage:
   *
   * <pre>
   * public static void main(String[] args) {
   *   Thread.currentThread().setUncaughtExceptionHandler(UncaughtExceptionHandlers.systemExit());
   *   ...