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From: lwall@jpl-devvax.jpl.nasa.gov (Larry Wall)
Newsgroups: comp.unix.shell,comp.lang.perl
Subject: Re: deleting some empty lines with sed
Message-ID: <1991May2.191157.6715@jpl-devvax.jpl.nasa.gov>
Date: 2 May 91 19:11:57 GMT
References: <1991Apr27.143519.26256@daimi.aau.dk> <281DB41B.9E6@marob.uucp>
Reply-To: lwall@jpl-devvax.JPL.NASA.GOV (Larry Wall)
Organization: Jet Propulsion Laboratory, Pasadena, CA
Lines: 25

In article <281DB41B.9E6@marob.uucp> daveh@marob.uucp (Dave Hammond) writes:
: Perhaps I'm oversimplifying the problem, but wouldn't
: 
: tr -s '\012'
: 
: squeeze multiple, consecutive newlines to a single newline?

Yes, it would, and yes, you are.  They wanted to squeeze 3 or more
consecutive newlines down to 2.

Incidentally, with perl 3.044 and later you can do it with

	perl -00pe 's/^\n+//'

or, less efficiently (because of file slurping overhead and string copying
due to modifying the middle of a long string, and because the previous
solution uses anchored search),

	perl -0777pe 's/\n{3,}/\n\n/g'

Oddly enough, any octal number will work in place of 0777 except 012, which
would set the input delimiter to newline.

Larry Wall
lwall@netlabs.com