For operators that can be used in either a scalar or array context, failure is generally indicated in a scalar context by returning the undefined value, and in an array context by returning the null list. Each operator decides which sort of scalar it would be most appropriate to return. Some operators return the length of the list that would have been returned in an array context. Some operators return the first value in the list. Some operators return the last value in the list.
Some operators return a count of successful operations.
In general, they do what you want, unless you want consistency. Go to the first , previous , next , last section, table of contents .