Path: utzoo!utgpu!water!watmath!clyde!att!rutgers!mailrus!ncar!boulder!spot!wu
From: wu@spot.Colorado.EDU (WU SHI-KUEI)
Newsgroups: comp.unix.questions
Subject: Re: sed script to combine blank lines?
Keywords: sed
Message-ID: <4057@boulder.Colorado.EDU>
Date: 14 Oct 88 14:40:17 GMT
References: <192@vlsi.ll.mit.edu> <136@nascom.UUCP> <7372@megaron.arizona.edu>
Sender: news@boulder.Colorado.EDU
Reply-To: wu@spot.Colorado.EDU (WU SHI-KUEI)
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Organization: University of Colorado, Boulder
Lines: 52

In article <7372@megaron.arizona.edu> rupley@arizona.edu (John Rupley) writes:
>In article <136@nascom.UUCP>, rar@nascom.UUCP (Alan Ramacher) writes:
>> In article <192@vlsi.ll.mit.edu>, young@vlsi.ll.mit.edu (George Young) writes:
>> > Is there a 'sed' wizard out there?  I often want to take a big ascii file
>> > (like a .c file after cc -E) and collapse each group of 'blank' lines
>> > into exactly one blank line.  'Blank' here is any combination of blanks,
>> > tabs and maybe ^L's.
>> 
>> sed is not powerful enuf for the job, but a simple awk script will
>> work. 
>
>The following simple sed script should work (after replacing <sp> etc
>by the corresponding ascii characters) -- and I suspect it is shorter and
>will run faster than an equivalent awk script.
>
>sed   "/^[<sp><tab><lf>]*$/{
>	N
>	/\n.*[^<sp><tab><lf>]/{
>	b
>	}
>	D
>	}" filename

Just to confirm the above I timed the following sed and awk scripts
on an otherwise empty 3B2/400 running SV3.1. The sed version is
approximately 35% faster when applied to a file which contains 948 and 250
lines before and after stripping off the extra blank lines.


------------------------------ cut here ------------------------------
sed -n '
/^[	]*$/ {
	p
: loop
	n
	/^[ 	]*$/b loop
}
/[!-~][!-~]*/p' $*
------------------------------ cut here ------------------------------

------------------------------ cut here ------------------------------
awk '
	BEGIN					{ empty = 1 }
	$0 !~ /^[ \t]+$|^$/			{print; empty = 0}
	$0 ~ /^$|^[ \t]+$/ && empty == 0	{print; empty = 1}
' $*
------------------------------ cut here ------------------------------

Just a guest here.  In real life
Carl Brandauer
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