Yes, that occurred to me later.

Still, to follow the Principle of Least Astonishment, I'd like to be able to specify a regex. To avoid further if then's, I'd probably set the default like so:

my $sep = q/' '/;
$sep = shift @ARGV if @ARGV; # you get the idea
my $line = "   one two three   \n";
my @words = eval qq(split $sep, \$line);
[download]

Then something evaluating to a regex must be used, such as:

$sep = q(/\s+/);
$sep = q(//);
$sep = q(/two|\s+/);
$sep = q(m|/|);
[download]

But the delimiters must be part of the string.

(I'm ignoring for now the security issue of letting the user specify a regex, as this is a script just for me. And I'm not up to untainting the full regex language, so I can't see letting this into the wild hands of colleagues.)