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Subject: RE: Buffering problem in netcat server script
Date: Tue, 11 Sep 2012 12:34:28 +0000
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Sven Severus wrote:
> Question 1:
> Why do I face different behaviour with "cat -n" and "sed s/e/E/g"?
> Are there cygwin related reasons?
> Which behaviour should I expect (I know there are buffering
> mechanisms for stdout when not connected to a tty, so I tend to
> say the buffering behaviour ist the one to expect).
>
> Question 2:
> What can I do to turn off the buffering behaviour and to get the
> output lines immediately?
> Or is my server script approach inappropriate? What should work
> better?

From `mad sed`:

    -u, --unbuffered

        load minimal amounts of data from the input files and flush the output
        buffers more often

If you add the -u option, sed will buffer less and write to the pipe more
often.  I would guess this isn't the default as it's less efficient, but
haven't done anything to verify that.

I believe `cat` never buffers, but I base this on nothing but instinct.

A quick experiment on my handy RHEL box implies this is not Cygwin specific;
the following command shows buffering behaviour too:

    tail -f tmpfile | sed 's/e/E/g' | tee outfile

(I'm using the pipelines so I can see what's going on without sed thinking
stdin or stdout are a terminal.)

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