If the problem here is that you need to know how to read a specific number of bytes for some pre-defined record size, you can use Perl's built-in read() function:

my $REC_SIZE = 16; # 16 byte records.
my $buf;           # location to store records
my @records;       # array of records.

while (read FH, $buf, $REC_SIZE) {
    push @records, $buf;
}
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You may also need to use binmode() depending on your operating system. And btw, you can use Perl's length() function to determine the size of scalars.