#!/usr/bin/perl -w
use strict;
my $str = '012345678901234567890123456789';
my @arr1 = $str =~ /(\d{5})/g;
my @arr2;
while (@arr1) { push @arr2, join('-', splice(@arr1,0,3)) }
print join('<br>',@arr2),$/;
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Output:

01234-56789-01234<br>56789-01234-56789
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