Date: Mon, 24 Sep 2007 20:52:17 -0700 From: Gary Kline <kline@tao.thought.org> To: Howard Goldstein <hg@queue.to> Cc: Gary Kline <kline@tao.thought.org>, freebsd-questions@freebsd.org Subject: Re: sed question... Message-ID: <20070925035217.GC50519@thought.org> In-Reply-To: <46F87B68.6090607@queue.to> References: <20070925013723.GA50027@thought.org> <46F87B68.6090607@queue.to>
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On Mon, Sep 24, 2007 at 11:07:20PM -0400, Howard Goldstein wrote:
> Gary Kline wrote:
> > My earlier post about deleting the first N lines was answered by
> > this one-liner site {below}. I wasn't including any
> > redirection; doing so finally resolved the problem. Now I need
> > to delete every line from the 19th or so to the last line.
> > Question one, can anybody explain the following syntax? What do
> > "P", "D" "ba" represent, in other words?
> >
> >
> > # delete the last 10 lines of a file
> > sed -e :a -e '$d;N;2,10ba' -e 'P;D' # method 1
> > sed -n -e :a -e '1,10!{P;N;D;};N;ba' # method 2
> >
> >
> > Question two, can sed do its thing inline?
>
> Wouldn't it be easier to use head -n 18 ?
>
No, because most of these files are between 40 and 50 lines. I
only care about the first 30 or 40; everything below has to be
deleted. By hand, using vi, I might type :31,$d that fixes
that one file. Of course, I could simply edit in "19" for
"10" above. It would be more savvy to understand the sed syntax.
--
Gary Kline kline@thought.org www.thought.org Public Service Unix
http://jottings.thought.org http://transfinite.thought.org
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