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From: rbj@uunet.UU.NET (Root Boy Jim)
Newsgroups: comp.unix.questions
Subject: Re: Inserting Blank Line into File (sed/awk/?)
Message-ID: <126604@uunet.UU.NET>
Date: 28 Mar 91 01:27:13 GMT
References: <807@oss670.UUCP> <ED.91Mar15201957@lvw6.lvw.loral.com> <3085@inews.intel.com>
Organization: UUNET Communications Services, Falls Church, VA
Lines: 17

>In article <ED.91Mar15201957@lvw6.lvw.loral.com> ed@lvw6.lvw.loral.com (Ed Allen) writes:
>>Now for the 'sed' solution....
>>sed -n -e '{N;N;p;a\
>>
>>}' filename

Most of it anyway. Works if the number of lines is a multiple of three.
Extra line or two gets eaten.

Anyway, here's a single line solution without the same bug:

	sed -n -e '$p;N;$p;N;h;s/.*//;H;x;p'

I think TC is right about avoiding sed in cases like this.
-- 
		[rbj@uunet 1] stty sane
		unknown mode: sane