How about this?

NB untested 
use strict;
use warnings;
use autodie;

my $filename = '...some filename...';

my $rangeStart = 10_000;
my $rangeEnd   = 20_000;

open my $fh, "<", $filename;
binmode $fh;

seek($fh, $rangeStart, 0);

my $total_bytes_to_read = $rangeEnd - $rangeStart + 1;
my $buffer_size = 1_024;
my $buffer;

my $num_bytes_to_read;
my $num_bytes_actually_read;

# read() : Returns the number of characters actually read, 0 at end of
+ file, or undef if there was an error (in the latter case $! is also 
+set)

while   (
            ( $num_bytes_to_read = ($buffer_size <= $total_bytes_to_re
+ad) ? $buffer_size : $total_bytes_to_read ),  # handle partial buffer
            ( $num_bytes_actually_read = read($fh, $buffer, $num_bytes
+_to_read) ),
            ( (defined $num_bytes_actually_read) && ($num_bytes_actual
+ly_read > 0) )
        )
{
    $total_bytes_to_read -= $num_bytes_actually_read;

    # process $num_bytes_actually_read in $buffer
}

if ( ! defined $num_bytes_actually_read )  { die $! }  # there was an 
+error.  In this example, autodie will detect this, but
                                                       #              
+        without autodie you'd need to check it yourself.

( $num_bytes_actually_read == 0 ) || die "Should never happen";

# if $total_bytes_to_read > 0, then reached EOF before reading all spe
+cified data
# ie $rangeEnd > size of $filename

[download]

In reply to Re: Byte ranges of binary files by zork42
in thread Byte ranges of binary files by PearlsOfWisdom

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.