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while-loop and reading over EOF?

I hope this is the correct list to ask my question - otherwise, please ignore.

I wonder whether anyone could explain the following OS X specific odd behaviour to me. I have the following simple perl script test.pl:

-----------------------------------------
#!/usr/bin/perl

undef $/;

$path = '/path/to/some/file.txt';

open(H, "<$path") || die("Couldn't open file: $path");
while (<H>) {
warn "got here";
$file=$_;
$length = length($file);
warn $length;
}
close(H);

exit(0);
-----------------------------------------

Under linux, this works fine - "undef $/" causes the whole file to be sucked in at once (because no record separator is defined) and $file contains what it would be expected to. I'm aware that it is of course in this case nonsense to put this into a while-loop - but it has brought my attention to the following behaviour under OS X - here's the output I get when running the above script:

got here at test.pl line 9, <H> chunk 1.
20508 at test.pl line 12, <H> chunk 1.
got here at test.pl line 9, <H> chunk 2.
0 at test.pl line 12, <H> chunk 2.

In other words - the while-loop is executed twice. It's as if EOF was different under OS X from Linux but perl doesn't know about it (or something like that?)....

If I change the second line to

$/ = \x04; # (or something else I know that doesn't exist in the file...)

then the while-loop is only executed once.

Any hints, suggestions, etc?
Thanks in advance!
Sebastian
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