Learning Perl, 5th Edition

Nonscalar Return Values

A scalar isn’t the only kind of return value a subroutine may have. If you call your subroutine in a list context,^[†] it can return a list of values.

Suppose you wanted to get a range of numbers (as from the range operator, ..), except that you want to be able to count down as well as up. The range operator only counts upward, but that’s easily fixed:

sub list_from_fred_to_barney {
  if ($fred < $barney) {
    # Count upwards from $fred to $barney
    $fred..$barney;
  } else {
    # Count downwards from $fred to $barney
    reverse $barney..$fred;
  }
}
$fred = 11;
$barney = 6;
@c = &list_from_fred_to_barney; # @c gets (11, 10, 9, 8, 7, 6)

In this case, the range operator gives us the list from 6 to 11, then reverse reverses the list so that it goes from $fred (11) to $barney (6), just as we wanted.

The least you can return is nothing at all. A return with no arguments will return undef in a scalar context or an empty list in a list context. This can be useful for an error return from a subroutine, signaling to the caller that a more meaningful return value is unavailable.

^[†] You can detect whether a subroutine is being evaluated in a scalar or list context using the wantarray function, which lets you easily write subroutines with specific list or scalar context values.