Example Drush commandfile. Place it in $HOME/.drush or /usr/share/drush/commands or any other valid location and clear drush cache afterwards.

mycommands.drush.inc

<?php
 
function mycommands_drush_command() {
  $items = array();
  $items['one-command'] = array(
    'description' => 'A command requiring two arguments.',
    // Declare required arguments.
    'arguments' => array(
      'arg1' => 'arg1 description',
      'arg2' => 'arg2 description',
    ),
  );
  $items['other-command'] = array(
    'description' => 'Description for this command.',
    // Declare options (as their name implies, are optional).
    'options' => array(
      'opt1' => 'opt1 description',
      'opt2' => 'opt2 description',
    ),
  );
  return $items;
}
 
/**
 * Callback for command one-command.
 *
 * Receive required command arguments as function parameters.
 */
function drush_mycommands_one_command($arg1, $arg2) {
  // ...
}

/**
 * Callback for command other-command.
 */
function drush_mycommands_other_command() {
  // A command doesn't declare arguments but can receive a variable number of them.
  $args = func_get_args();

  // Get option1.
  $opt1 = drush_get_option('opt1', 'default-value');
}