php.install

<?php

/**
 * Implementation of hook_install().
 */
function php_install() {
  $format_exists = db_result(db_query("SELECT COUNT(*) FROM {filter_formats} WHERE name = 'PHP code'"));

  // Add a PHP code input format, if it does not exist. Do this only for the
  // first install (or if the format has been manually deleted) as there is no
  // reliable method to identify the format in an uninstall hook or in
  // subsequent clean installs.
  if (!$format_exists) {
    db_query("INSERT INTO {filter_formats} (name, roles, cache) VALUES ('PHP code', '', 0)");
    $format = db_result(db_query("SELECT MAX(format) FROM {filter_formats}"));

    // Enable the PHP evaluator filter.
    db_query("INSERT INTO {filters} (format, module, delta, weight) VALUES (%d, 'php', 0, 0)", $format);
    drupal_set_message(t('A !php-code input format has been created.', array(
      '!php-code' => l('PHP code', 'admin/settings/filters/' . $format),
    )));
  }
}

/**
 * Implementation of hook_disable().
 */
function php_disable() {
  drupal_set_message(t('The PHP module has been disabled. Please note that any existing content that was using the PHP filter will now be visible in plain text. This might pose a security risk by exposing sensitive information, if any, used in the PHP code.'));
}