{
my $splitter= qr/\d+|[A-Za-z]+|[^0-9A-Za-z]+/;
sub compare_version_string ($$)
# returns <0, 0, >0 to indicate less, eq, or greater-than.
# dies (exception) if no relation exists.
 {
 my ($left, $right)= @_;
 my @left= $left =~ /$splitter/g;
 my @right= $right =~ /$splitter/g;
 print "@left\n";
 print "@right\n";
 my $r;
 while (@left && @right) {
    $left= shift @left;
    $right= shift @right;
    if ($left =~ /^\d+$/ && $right =~ /^\d+$/) {
       # compare as numbers
       $r= $left <=> $right;
       return $r  if $r;  # or keep going if zero.
       }
    elsif ($left =~ /^[A-Za-z]+$/ && $right =~ /^[A-Za-z]+$/) {
       # compare as strings
       $r= $left cmp $right;
       return $r  if $r;  # or keep going if zero.
       }
    elsif ($left =~ /^[^0-9A-Za-z]+$/  &&  $right =~ /^[^0-9A-Za-z]+$/) {
       # delimter or "other", much match exact.
       die "version strings are not compatible.\n"  unless $left eq $right;
       }
    else {
       # the parts are not of the same type
       die "version strings are not compatible.\n";
       }
    }
 # one of the strings ran out of parts.
 return scalar(@left) <=> scalar(@right);
 }
}