A math way: (added two test cases for possible boundary problem)

use strict;
use warnings;

sub elide {
    my ($start,$end) = @_;
    if ((my $diff1 = length($end) - length($start)) > 0) {
        return "$start-$end";
    } elsif ($diff1 == 0) {
        if ($start == $end) {
            return $start;
        } else {
            if ((my $diff2 = length($end) - length($end - $start)) > 0
+) {
                $end %= 10 ** (length($end) - $diff2);
            } 
            return "$start-$end";
        }
    }
}

while ( <DATA> ) {
  print elide( split ' ', $_ ), "\n";
}

__DATA__
1   32
4   19
28  39
34  123
321 321
324 329
325 349
340 509
999 1000
1000 1001

[download]

I tried to do it more math by using log10 to determine length, but that failed the second test case I added, because of rounding issue.

In reply to Re: eliding number ranges by pg
in thread eliding number ranges by qq

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