WP_CLI::error() │ public static │ WP-CLI 1.0

Display error message prefixed with "Error: " and exit script.

Error message is written to STDERR. Defaults to halting script execution with return code 1.

Use WP_CLI::warning() instead when script execution should be permitted to continue.

# `wp cache flush` considers flush failure to be a fatal error.
if ( false === wp_cache_flush() ) {
	WP_CLI::error( 'The object cache could not be flushed.' );
}

Method of the class: WP_CLI{}

No Hooks.

Return

null. Nothing (null).

Usage

$result = WP_CLI::error( $message, $exit );
$message(string|WP_Error|Exception|Throwable) (required)
Message to write to STDERR.
$exit(true|false|int)
True defaults to exit(1).
Default: true

WP_CLI::error() code WP-CLI 2.8.0-alpha

wp-cli/php/class-wp-cli.php 
public static function error( $message, $exit = true ) {
	if ( null !== self::$logger && ! isset( self::get_runner()->assoc_args['completions'] ) ) {
		self::$logger->error( self::error_to_string( $message ) );
	}

	$return_code = false;
	if ( true === $exit ) {
		$return_code = 1;
	} elseif ( is_int( $exit ) && $exit >= 1 ) {
		$return_code = $exit;
	}

	if ( $return_code ) {
		if ( self::$capture_exit ) {
			throw new ExitException( null, $return_code );
		}
		exit( $return_code );
	}
}