sort + head = weirdness?

From: Mark (unixadmin_at_livebridge.com)
Date: 10/02/03 

Date: Wed, 01 Oct 2003 15:29:17 -0700

This is really weird. I'm catting a text file, piping it through
'sort'and then through 'head' and I'm getting really strange results.

This only affects files > 4096 bytes.
It's only a problem when piping through 'head'; 'tail' works fine.
It's only a problem when piping through a file containing 'sort'; it
works fine with 'sort' itself.

(The test file is just a text file containing the numbers 1-9 repeated.)
('format' is a file containing the single word 'sort'. Eventually this
will contain other formatting commands.)

So, here's what happens:

With a file 4096 bytes or less it works fine.
# ls -al testfile -rw-rw-r--
   1 root root 4096 Oct 1 14:46 testfile

# cat testfile | format | head -1
12345

If I add one more character to the file, it fails.
# ls -al testfile
-rw-rw-r-- 1 root root 4097 Oct 1 14:38 testfile

# cat testfile | format | head -1
123456
/usr/local/bin/drs/format: line 1: 8688 Broken pipe sort

If, with the same 4097 byte file I replace 'head' with 'tail', it works
fine.
# cat testfile | format | tail -1
123456789

If I replace 'format' with 'sort' it works fine.
# cat testfile | sort |head -1
123456

Any idea what's going on here? Is there some buffer somewhere that can
only take 4k of data?

Mark

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