I recently had this same problem. Not realizing there might be a CPAN module (I know, I know, what was I thinking?), I came up with this sub:

sub expandlist {
  local $" = '..';  # locally set list separator
  my (@parts);
  sort {$a <=> $b}
    map {
      map {
        ((@parts = split /-/) == 2) ? eval('map {$_} '. "@parts") : $_
      } split /,/
    } @_;
}
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Briefly:

• The outer map loops through all function args (usually only called with one). For each arg, split on commas.
• Try to split each element originally separated by commas, on hyphens.
• If splitting on hyphens produces exactly two elements in @parts, interpolate the array into a string (with the list separator set to '..'), turning, e.g., '6-9' into '6..9' which is appended to 'map {$_}' and that whole thing eval'ed, ultimately producing a list of elements: 6, 7, 8, 9
• The elements are all gathered and combined and sorted.

Crude and hardly idiot-proofed, but it works without having to get a CPAN module installed on all our servers.