Date: Tue, 25 Sep 2007 09:31:04 +0300 From: Nikos Vassiliadis <nvass@teledomenet.gr> To: freebsd-questions@freebsd.org Cc: Howard Goldstein <hg@queue.to>, Gary Kline <kline@tao.thought.org> Subject: Re: sed question... Message-ID: <200709250931.05367.nvass@teledomenet.gr> In-Reply-To: <46F87B68.6090607@queue.to> References: <20070925013723.GA50027@thought.org> <46F87B68.6090607@queue.to>
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On Tuesday 25 September 2007 06:07, 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.
sed -e 18q
that is, quit after processing line 18.
> > Question one, can anybody explain the following syntax? What do
> > "P", "D" "ba" represent, in other words?
The manual page explains sed in a very good way. For sure, better
than I could describe it here. You'd better read it.
> >
> >
> > # 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?
Yes.
-i extension
Edit files in-place, saving backups with the specified extension.
If a zero-length extension is given, no backup will be saved. It
is not recommended to give a zero-length extension when in-place
editing files, as you risk corruption or partial content in situ-
ations where disk space is exhausted, etc.
>
> Wouldn't it be easier to use head -n 18 ?
No, it's the same. Some sed operation are trivial to read/write,
others aren't.
HTH
Nikos
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