So, instead of sketching why don't you draw an outline? Something like:

use strict;
use warnings;

my $fileName = "sample.dat";
open my $inFile, '<:raw', $fileName or die "Can't open '$fileName': $!
+\n";

my $loc = 23;
my $len = 20;
my $bytes;

seek $inFile, $loc, 0; 
read $inFile, $bytes, $len;

...
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