/**
 * Parses given expression or undefined if invalid.
 *
 * @category Parsers
 * @example
 * ```typescript
 * parseStringUnixExpression("1 1 1 1 1"); // ["1", "1", "1", "1", "1"]
 * parseStringUnixExpression(" 1   1    1    1   1 "); // ["1", "1", "1", "1", "1"]
 * parseStringUnixExpression("1 1 1 1 1 1"); // undefined
 * parseStringUnixExpression("1 1 1 1"); // undefined
 * ```
 * @param source string to be parsed.
 * @returns An array of 5 elements or `undefined` if invalid.
 */
export declare const parseStringUnixExpression: (
	source: string,
) =>
	| readonly [
			minutes: string,
			hours: string,
			dayOfMonth: string,
			month: string,
			dayOfWeek: string,
	  ]
	| undefined;