The size of reads for buffered I/O is configurable (since 5.014), but only when Perl is compiled.

You could use syread instead of buffered I/O. 

$ strace perl -e'1 while read(STDIN, $buf, 512)' <a 2>&1 | grep 'read(
+0'
read(0, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"..., 8192) = 8192
read(0, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"..., 8192) = 8192
read(0, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"..., 8192) = 3616
read(0, "", 8192)                       = 0

$ strace perl -e'1 while sysread(STDIN, $buf, 512)' <a 2>&1 | grep 're
+ad(0'
read(0, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"..., 512) = 512
read(0, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"..., 512) = 512
read(0, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"..., 512) = 512
read(0, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"..., 512) = 512
read(0, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"..., 512) = 512
read(0, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"..., 512) = 512
read(0, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"..., 512) = 512
read(0, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"..., 512) = 512
read(0, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"..., 512) = 512
read(0, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"..., 512) = 512
read(0, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"..., 512) = 512
read(0, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"..., 512) = 512
read(0, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"..., 512) = 512
read(0, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"..., 512) = 512
read(0, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"..., 512) = 512
read(0, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"..., 512) = 512
read(0, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"..., 512) = 512
read(0, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"..., 512) = 512
read(0, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"..., 512) = 512
read(0, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"..., 512) = 512
read(0, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"..., 512) = 512
read(0, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"..., 512) = 512
read(0, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"..., 512) = 512
read(0, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"..., 512) = 512
read(0, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"..., 512) = 512
read(0, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"..., 512) = 512
read(0, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"..., 512) = 512
read(0, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"..., 512) = 512
read(0, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"..., 512) = 512
read(0, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"..., 512) = 512
read(0, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"..., 512) = 512
read(0, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"..., 512) = 512
read(0, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"..., 512) = 512
read(0, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"..., 512) = 512
read(0, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"..., 512) = 512
read(0, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"..., 512) = 512
read(0, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"..., 512) = 512
read(0, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"..., 512) = 512
read(0, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"..., 512) = 512
read(0, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx", 512) = 32
read(0, "", 512)                        = 0

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In reply to Re: Perl reads minimum 8KB from files. Can this be lowered? by ikegami
in thread Perl reads minimum 8KB from files. Can this be lowered? by sectokia

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