Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!samsung!think.com!mintaka!ogicse!unmvax!crowley
From: crowley@unmvax.cs.unm.edu (Charlie Crowley)
Newsgroups: comp.editors
Subject: Re: Global Empty Line Removal in vi?
Message-ID: <1991Jan30.001551.7538@unmvax.cs.unm.edu>
Date: 30 Jan 91 00:15:51 GMT
References: <1991Jan24.163844.7521@unmvax.cs.unm.edu> <1991Jan26.233521.17721@ddsw1.MCS.COM> <1991Jan27.073848.27626@ddsw1.MCS.COM>
Sender: crowley@unmvax.cs.unm.edu
Organization: University of New Mexico
Lines: 49

Well, the first time I read this I misunderstood and thought he wanted to
get rid of all blank lines.  I looked at the title and not closely enough
at the text.  Getting rid of all but one is harder.  Solutions so far:

(1) filtering through cat -s (on bsd systems)
(2) using awk -- pretty easy if you know awk
(3) using sed -- somewhat complex 

I found a way (albeit complex) to do it from within vi.

(1) find a string that does not occur anywhere in the text.  I will use
'qqq' below.  It is easy to check by searching for it and getting a failure.
	/qqq

(2) replace all blank lines withi this string
	:g/^$/s/^/qqq/

(3) Join all such lines.  This must be done one step at a time where
each step joins half of the remaining lines.
	:g/qqq$/j
	:g/qqq$/j
	:g/qqq$/j
	:g/qqq$/j
You have to do it until it does not affect any lines.  The four above will
work if no run of blank lines is more than 32 blank lines.  If you
	:set report=1
you will find out whether it affected any lines.
At this point all the 'qqq 's for each run of blank lines are all on
the same line.  The ' ' is a side effect of the join (j).

(4) Replace the first one of these with a newline.
	:%s/qqq /^M/
where the '^M' was produced by ^V then ^M.  There are no control characters
in the above two lines for this presentation but they are needed when
you type the command into vi.

(5) Remove all the extra 'qqq 's.
	:%s/qqq //g

Okay, it is complex. It did it in X by having the command lines in a file
and copying them into vu using the X selection.  I tried combining them
into a macro but I got confused in a morass of ^Vs.  Maybe someone more
expert in vi :map's can tell me how to do it.

The two flaws are the need to find a unique string (minor) and the need to
iterate the step (3) command.

Charlie Crowley
Univ. of New Mexico Computer Science Department