What if your range isn't a whole number of $readsz chunks?

I'd do something like this :-

    while ($myrange) {
        $myrange -= read($fh, $buf, min($myrange,$readsz) ) or last;
        # do stuff
    }
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> What if your range isn't a whole number of $readsz chunks? Shows the use of a second pair of eyes ! Thank you ! ;-) Will go try ....

Question... doesn't last stop the processing prematurely before the rest of the while block gets a chance to execute ?

No.

what do you think the 'or' is doing in that statement?

hint: Have a look at at 'logical or' in perlop

my $myRange = $rangeEnd - $rangeStart;
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my $myRange = $rangeEnd - $rangeStart + 1;
                                      ^^^
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Re: Also, do you have an off-by-1 error? Hmm .... I spend hours on end staring at my computer screen and trying all the examples posted here and I still couldn't get the program to work like I think it should be. ;-(

Perhaps I'll go back to my initial code and try with the amended range. Will let you know how it goes.

Is this the correct...

$myRange  ne  $readSz?

The idea in my brain was that $myRange = the range of bytes required, and $readSz = the buffer size. But maybe that got lost in translation into Perl ?

You could try something like:

use constant READSIZE => ...;

my $fh = ...;
my $start = ...;
my $end   = ...; ## check $end < -s($fh)!

seek $fh, $start, 0;
while( ($_ = tell( $fh ) ) < $end ) {
    local $/ = \min( READSIZE, $end - $_ );
    my $chunk = <$fh> or die $!;
    ## ...
}
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---

With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.

"Science is about questioning the status quo. Questioning authority".

In the absence of evidence, opinion is indistinguishable from prejudice.

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
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