You could use a look-ahead.

use strict;
use warnings;

my @nos = qw{
   12304500
   123
   1234567000000
   987045027000
};

print
   map { sprintf qq{%15s : %5s\n}, @$_ }
   map { [ $_, m{(\d{1,5})(?=0*\z)} ] }
   @nos;
[download]

Here's the output.

       12304500 : 23045
            123 :   123
  1234567000000 : 34567
   987045027000 : 45027
[download]

I hope this is of use.

Cheers,

JohnGG

Update: No, that doesn't work unless you make the \d{1,5} non-greedy, as suggested by duff