Re: grep | sed do not function inline?
- From: Mike Bird <mgb-debian@xxxxxxxxxxxx>
- Date: Sun, 22 Apr 2007 17:30:11 -0700
On Sunday 22 April 2007 16:13, bilbo wrote:
Recently I faced a strange behaviour of the Linux commands. I have a
log file which contains a lot of information. I wanted to extract some
informations out of it. But when I tried to
tail -f mylog | grep 'smtg' | sed -n 's/end/notend/p'
no output could be found. Which was quite surprising since the
following tests did their job without any problem:
tail -f mylog | grep 'smtg'
tail -f mylog | sed -n 's/end/notend/p'
tail -200 mylog | grep 'smtg' | sed -n 's/end/notend/p'
So, of course, to achieve this result I simply went for perl. But can
anyone tell me what is the reason why this didn't work?
You did not wait for grep's output buffer to fill and send the
first output to sed. Add the --line-buffered switch to the grep
command, or use:
tail -f mylog | sed -n '/smtg/s/end/notend/p'
--Mike Bird
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