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Old 08-31-2006, 03:48 PM   #1
Registered: Aug 2006
Posts: 34

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Sed gives output in pipes only when buffer is full

Hi !
I basicly tried to run the following command :
command | sed -e 's/something/something else/' | command_2
snd it gives the output in huge chunks instead of nicely giving output lines at the input lines' speed.

By playing a little with things like :
sed something | cat
I understood that it only gave the output when the buffer (8192 chars) was full. But it works fine with no redirection after sed.
I read half of /usr/share/doc/sed-*/index.html (or similar) but couldn't find anything mentionning this.

I tried with variants of :
sed -e 's/a/b/; p'
sed -n -e 's/a/b/; p'
but it's still doesn't work.

Could someone tell me how to explain to sed that I want it to spit out each line of input to the output without stupidly waitig; to be nice like it is without any redirection afterwards ???

BTW. The bug is only visible if the input isn't in one whole chunk, you should put a few usleep's in the input in order to reproduce the bug.
Old 08-31-2006, 04:06 PM   #2
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Although I doubt that sed is the problem, here's a way to 'check': Use sed's -u (--unbuffered) option and see what happens.

I've seen this behavior before, but sed was not the problem, the command before/after the pipe was, that's the reason for doubt about sed being the problem.

Anyway, hope this gets you going again.
Old 08-31-2006, 05:57 PM   #3
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Registered: May 2006
Location: Frankfurt, Germany
Distribution: SUSE 10.2
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