my $str = '';
my $tmp;
while (read($handle, $tmp, 32*1024)) {
    $str .= $tmp;
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can be written as

my $str = '';
while (read($handle, $str, 32*1024, length($str))) {
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Also,

pos($str) = 0;
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is already done by

$str = substr($str, pos($str));
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(Well, pos($str) = undef; is.)