This was a question on the perl quiz of the week that ran for a few months last year. Question #6 asks exactly what you are looking for.

Here is MJDs summary.

The shortest solution was provided by Andreas Koenig:

use Set::IntSpan; # CPAN rules :-)
use strict;

sub expand_number_list {
    my $run = shift;
    my $set = Set::IntSpan->new($run);
    $set->elements;
}
[download]

Here is a list of everyone else's submisions.

Update: Silly me, I included Andreas' answer for expand_number_list by mistake! Here is the one you are looking for:

use Set::IntSpan; # CPAN rules :-)
use strict;
sub format_number_list {
  my(@n) = @_;
  my $set = Set::IntSpan->new(join ",", @n);
  my $run = $set->run_list;   
  $run =~ s/,/, /g; # give them the spaces
  $run;
}
[download]