Re: bin/51171: sed does not match newlines in regexps properly

[Robert Elz <kre%munnari.OZ.AU@localhost>]

The following reply was made to PR bin/51171; it has been noted by GNATS.

From: Robert Elz <kre%munnari.OZ.AU@localhost>
To: gnats-bugs%NetBSD.org@localhost
Cc: 
Subject: Re: bin/51171: sed does not match newlines in regexps properly
Date: Fri, 27 May 2016 16:16:57 +0700

     Date:        Fri, 27 May 2016 07:40:00 +0000 (UTC)
     From:        jarle%uninett.no@localhost
     Message-ID:  <20160527074000.50F8B7AABE%mollari.NetBSD.org@localhost>
 
 
   | -------- script.sed ---------
   | 1{h;d;}
   | 2{H;d;}
   | 3{H
   |   x
   | # Pattern space: line1 \n line2 \n \line3 (without spaces)
   | # Now, delete the first character of line1 and line2
   |   s/^[^\n]\([^\n]*\n\)[^\n]/\1/
   | }
   | -----------------------------
   | 
   | On NetBSD 6, the command
   |   (echo abc; echo def; echo ghi) | sed -f script.sed
   | will print:
   | bc
   | ef
   | ghi
   | which is what I would expect.
 
 If it does it is a bug the expression [^\n] matches a character
 that is neither a '\' nor an 'n' and has nothing at all to do with newlines.
 No escape characters work inside [] (though there a whole set of
 magic combinations that mean specific things).
 
 As best I can tell (having looked for it for ages) there is no way in
 sed to match anything other than a newline.   I resorted to s/\n/X/
 where X was a character I knew could not appear in the text (because
 earlier commands had removed all instances), followed by [^X] in the
 expression to do the work, followed by s/X/${nl}/ (${nl} is a literal
 newline.   Truly ugly, but I believe the only way possible.
 
 The best solution I can think of is to add a new char class that contains
 just newline, say [:nl:] and then use [^[:nl:]] but no sed does anything
 like that that I am aware of.
 
 kre