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From: Kenny McCormack on 27 Apr 2010 12:40
In article <hr721b$3ur$1(a)speranza.aioe.org>,
aioe <worKEEPSPAMOUTwor(a)bellsouth.net> wrote:
>On 4/27/2010 9:07 AM, Janis Papanagnou wrote:
>> NR>1 && !/regexp/ { print "" }
>> { printf "%s", $0 }
>> END { print "" }
>
>Thanks. That works, though I would have to spend some time with my awk
>book to figure out why.
>
>Suppose I wanted to replace the deleted newlines with tabs?
>

You can always try this:

# ll stands for "last line"
NR > 1 { ORS=/regexp/?"\t":"\n";print ll }
{ ll = $0 }
END { if (ll) print ll }
# Note that if the regexp is present in the last line, then the last
# line won't be terminated with a newline. This is per spec, but may
# not be desirable.

--
(This discussion group is about C, ...)

Wrong. It is only OCCASIONALLY a discussion group
about C; mostly, like most "discussion" groups, it is
off-topic Rorsharch [sic] revelations of the childhood
traumas of the participants...

From: Ed Morton on 27 Apr 2010 13:00
On Apr 27, 9:51 am, aioe <worKEEPSPAMOUT...(a)bellsouth.net> wrote:
> Is there an easy way to replace the *previous* newline when a line
> contains a regexp match?  I suspect awk is the right tool for this, but
> I'm not very familiar with awk. It appears to be possible, but very
> clumsy, to do this with sed. I know how to do it with an ed script, but
> I would like to pipeline.

awk '
{ printf "%s%s", (/regexp/ ? "" : n), $0; n="\n"}
END { print "" }
'

Ed.
From: Ed Morton on 27 Apr 2010 13:01
On Apr 27, 11:06 am, aioe <worKEEPSPAMOUT...(a)bellsouth.net> wrote:
> On 4/27/2010 9:07 AM, Janis Papanagnou wrote:
>
> >    NR>1 && !/regexp/ { print "" }
> >    { printf "%s", $0 }
> >    END { print "" }
>
> Thanks.  That works, though I would have to spend some time with my awk
> book to figure out why.
>
> Suppose I wanted to replace the deleted newlines with tabs?

awk '
{ printf "%s%s", (/regexp/ ? t : n), $0; t="\t"; n="\n"}
END { print "" }
'

Ed.
From: pk on 27 Apr 2010 13:02
aioe wrote:

> Thanks. I didn't make myself clear: I want to replace only the newline
> (with space, comma, tab or something) and not the whole previous line.
> For example, I would like to join the first two lines by replacing the
> newline that precedes [ with a space, but make no other changes, in the
> following example:
>
>
> TCP dell03:4407 mx02.eternal-september.org:nntp
> ESTABLISHED
> 2596
> [thunderbird.exe]
>
> TCP dell03:netbios-ssn 192.168.2.102:51042 TIME_WAIT 0
> TCP dell03:netbios-ssn 192.168.2.102:51041 TIME_WAIT 0


Ok, so you want "join line1 and line2 if line2 matches a pattern". Since
you've had awk solutions already, here is with sed (not because sed is
better, but because this is listed in the sed FAQ):

sed ':a; $!N;s/\n\([^\n]*pattern\)/\1/;ta;P;D'

GNU sed syntax.
From: Jon LaBadie on 27 Apr 2010 18:06
pk wrote:
> aioe wrote:
>
>> Is there an easy way to replace the *previous* newline when a line
>> contains a regexp match? I suspect awk is the right tool for this, but
>> I'm not very familiar with awk. It appears to be possible, but very
>> clumsy, to do this with sed. I know how to do it with an ed script, but
>> I would like to pipeline.
>
> Assuming your text does not appear on the very first line, with awk you can
> try this:
>
> awk '/pattern/{p="new text"}{print p}{p=$0}END{print p}' file
>
> With sed it's not so difficult (GNU sed syntax):
>
> sed -n '/pattern/{x;s/.*/new text/;x;};x;p;x;h;$p' file
>
> I can't test with ed now but I expect it to be quite simple too.
>

Here is one:

echo '2,$g/pattern/s/^/ /\
-1,.j
w
q' | ed - file

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