Hi, along Corion's suggestion but with a little bit of naive range-merging. HTH, although it looks a little bit C-ish...

use strict;
use warnings;

# valid ranges: 0..$max_line
my @err_ranges = qw(39887-399900 23-900 8000-10000 50000-1000500 40000
+-90000);
my $max_line   = 100000000;

# save b(egin) and e(nd) of ranges and sort by lower b(egin) of ranges
my @errs_b_e  = sort { $a->[0] <=> $b->[0] } map { m/(\d+)\-(\d+)/; [ 
+$1 , $2 ] } @err_ranges;

# merge overlapping and adjacent ranges
for (my $i=0; $i<$#errs_b_e; $i++) {
  my $cmp_a = $errs_b_e[$i];
  my $cmp_b = $errs_b_e[$i+1];
  my ($a_lo, $a_hi, $b_lo, $b_hi) = map { ($_->[0], $_->[1]) } ($cmp_a
+, $cmp_b);

  #overlapping? e.g. 10..20 15..25 --> 10..25
  if ($a_lo <= $b_lo and $b_lo <= $a_hi) {
    $cmp_b->[0] = $a_lo;         # lower bound defined by $a_lo
    $cmp_b->[1] = $a_hi > $b_hi ? $a_hi : $b_hi; # upper bound defined
+ by max.
    $cmp_a->[0] = -1             # taint LHS range
  } elsif ($a_hi == $b_lo-1) {   #adjacent? e.g. 10..20 21..22 --> 10.
+.22
    $cmp_b->[0] = $a_lo;         # lower bound defined by $a_lo
    $cmp_a->[0] = -1             # taint LHS range
  } #update/hint: the if/elsif above can be reduced ;-)
}

# remove tainted ranges, create list of inverse boundaries
my @merged =  map { $_->[0]-1 => $_->[1]+1 }  grep { $_->[0] >= 0 } @e
+rrs_b_e;

# edge-cases
$merged[0]  < 0          ?  shift @merged : unshift @merged, 0;
$merged[-1] > $max_line  ?  pop   @merged : push    @merged, $max_line
+;

for (my $i=0; $i<@merged; $i+=2) {
  print $merged[$i], "-", $merged[$i+1], "\n";
}
[download]

Prints:

pb> perl 752436.pl
0-22
901-7999
10001-39886
1000501-100000000
[download]