8.12.2. Solution

Once you know the record's size, multiply it by the record number to get the byte address, and then seek to that byte address and read the record:

$ADDRESS = $RECSIZE * $RECNO;
seek(FH, $ADDRESS, 0) or die "seek:$!";
read(FH, $BUFFER, $RECSIZE);

8.12.3. Discussion

The Solution assumes the first record has a RECNO of 0. If you're counting from one, use:

$ADDRESS = $RECSIZE * ($RECNO-1);

This is best applied to binary data. Applying it to text files assumes you have a constant character width and constant line length. This rules out most Unicode encodings, any kind of Windows text file, and any text file where lines can have different lengths.