> unpack  => sub { # Suggested but not implemented by pryrt

Actually unpack was suggested (and not implemented) by me first. ;)

FWIW: My idea was to unpack multiple lines simultaneously instead of going line by line.

If you are interested and all lines really have the same length (the OP never clarified)

• read a chunk of complete lines bigger 4 or 8kb (depending on the blocksize of the OS to optimize read operations)
• run a repeated unpack pattern
• get a list of 1 result for each chunk line

Please see if substr on single lines is still faster then.

$line_length += $newline_length;                 # OS dependend
$line_count   = int(8 * 1024 / $line_length) +1;
$chunk_size   = $line_count * line_length;
[download]

And yes I'm still reluctant to implement it, smells too much like an XY Problem :)

update

In hindsight... probably having a slightly smaller chunk is more efficient :

$line_count   = int(8 * 1024 / $line_length)

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