get_option

function get_option( $option, $default = false ) {
	global $wpdb;

	$option = trim( $option );
	if ( empty( $option ) ) {
		return false;
	}

	/*
	 * Until a proper _deprecated_option() function can be introduced,
	 * redirect requests to deprecated keys to the new, correct ones.
	 */
	$deprecated_keys = array(
		'blacklist_keys'    => 'disallowed_keys',
		'comment_whitelist' => 'comment_previously_approved',
	);

	if ( ! wp_installing() && isset( $deprecated_keys[ $option ] ) ) {
		_deprecated_argument(
			__FUNCTION__,
			'5.5.0',
			sprintf(
				/* translators: 1: Deprecated option key, 2: New option key. */
				__( 'The "%1$s" option key has been renamed to "%2$s".' ),
				$option,
				$deprecated_keys[ $option ]
			)
		);
		return get_option( $deprecated_keys[ $option ], $default );
	}

	/**
	 * Filters the value of an existing option before it is retrieved.
	 *
	 * The dynamic portion of the hook name, `$option`, refers to the option name.
	 *
	 * Returning a truthy value from the filter will effectively short-circuit retrieval
	 * and return the passed value instead.
	 *
	 * @since 1.5.0
	 * @since 4.4.0 The `$option` parameter was added.
	 * @since 4.9.0 The `$default` parameter was added.
	 *
	 * @param mixed  $pre_option The value to return instead of the option value. This differs
	 *                           from `$default`, which is used as the fallback value in the event
	 *                           the option doesn't exist elsewhere in get_option().
	 *                           Default false (to skip past the short-circuit).
	 * @param string $option     Option name.
	 * @param mixed  $default    The fallback value to return if the option does not exist.
	 *                           Default false.
	 */
	$pre = apply_filters( "pre_option_{$option}", false, $option, $default );

	if ( false !== $pre ) {
		return $pre;
	}

	if ( defined( 'WP_SETUP_CONFIG' ) ) {
		return false;
	}

	// Distinguish between `false` as a default, and not passing one.
	$passed_default = func_num_args() > 1;

	if ( ! wp_installing() ) {
		// Prevent non-existent options from triggering multiple queries.
		$notoptions = wp_cache_get( 'notoptions', 'options' );

		if ( isset( $notoptions[ $option ] ) ) {
			/**
			 * Filters the default value for an option.
			 *
			 * The dynamic portion of the hook name, `$option`, refers to the option name.
			 *
			 * @since 3.4.0
			 * @since 4.4.0 The `$option` parameter was added.
			 * @since 4.7.0 The `$passed_default` parameter was added to distinguish between a `false` value and the default parameter value.
			 *
			 * @param mixed  $default The default value to return if the option does not exist
			 *                        in the database.
			 * @param string $option  Option name.
			 * @param bool   $passed_default Was `get_option()` passed a default value?
			 */
			return apply_filters( "default_option_{$option}", $default, $option, $passed_default );
		}

		$alloptions = wp_load_alloptions();

		if ( isset( $alloptions[ $option ] ) ) {
			$value = $alloptions[ $option ];
		} else {
			$value = wp_cache_get( $option, 'options' );

			if ( false === $value ) {
				$row = $wpdb->get_row( $wpdb->prepare( "SELECT option_value FROM $wpdb->options WHERE option_name = %s LIMIT 1", $option ) );

				// Has to be get_row() instead of get_var() because of funkiness with 0, false, null values.
				if ( is_object( $row ) ) {
					$value = $row->option_value;
					wp_cache_add( $option, $value, 'options' );
				} else { // Option does not exist, so we must cache its non-existence.
					if ( ! is_array( $notoptions ) ) {
						$notoptions = array();
					}

					$notoptions[ $option ] = true;
					wp_cache_set( 'notoptions', $notoptions, 'options' );

					/** This filter is documented in wp-includes/option.php */
					return apply_filters( "default_option_{$option}", $default, $option, $passed_default );
				}
			}
		}
	} else {
		$suppress = $wpdb->suppress_errors();
		$row      = $wpdb->get_row( $wpdb->prepare( "SELECT option_value FROM $wpdb->options WHERE option_name = %s LIMIT 1", $option ) );
		$wpdb->suppress_errors( $suppress );

		if ( is_object( $row ) ) {
			$value = $row->option_value;
		} else {
			/** This filter is documented in wp-includes/option.php */
			return apply_filters( "default_option_{$option}", $default, $option, $passed_default );
		}