I found the problem in my loop, after use perl -d debugger, it is the $bytes_read should be "my $bytes_read", in the code, it is defined twice, it is a little bit confused, should have better clear way to do that, but in the code I have, it is like that, and when I rewrite the code, I remove my in frond $bytes_code in the while loop, which was wrong. So it should be

my $bytes_read = sysread($fh,$bug,$blocksize)
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