Function expand_alias 

pub fn expand_alias(s: &str) -> Result<String>

Expand cron alias strings (like @hourly, @daily 9:30) into standard 5-field cron expressions. Unrecognized strings are returned unchanged.

Alias	Parameter	Example	Expands to
@hourly	minute 0-59	@hourly 30	30 * * * *
@hourly	none	@hourly	0 * * * *
@daily	hour	@daily 9	0 9 * * *
@daily	hour:min	@daily 9:30	30 9 * * *
@daily	none	@daily	0 0 * * *
@weekly	day (0=Sun)	@weekly 1	0 0 * * 1
@weekly	none	@weekly	0 0 * * 0
@monthly	day-of-month	@monthly 15	0 0 15 * *
@monthly	none	@monthly	0 0 1 * *
@yearly	month-day	@yearly 3-15	0 0 15 3 *
@yearly	none	@yearly	0 0 1 1 *

Returns an error if a parameter is present but not a valid number, or is out of the accepted range for that field.