#!/usr/bin/perl -slw
use strict;

my $data = <<EOD;
record 1 is 20 bytesrecord 2 is 20 bytesrecord 3 is longer at 30 bytes
EOD

my $p = 0;
my @refs;

# endpos would be calculated based on recsize - this is simplified:
my @endpos=(20,40,70);

for (@endpos) {
   push @refs, \substr $data, $p, $_ - $p;
   $p = $_;
}
print '[',$$_,']' for @refs;