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Date: Thu, 17 Sep 2009 22:33:40 +0200
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From: Rudolf Sykora <rudolf.sykora@gmail.com>
To: Fans of the OS Plan 9 from Bell Labs <9fans@9fans.net>
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Subject: Re: [9fans] awk help; not plan9 matter
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2009/9/17 roger peppe <rogpeppe@gmail.com>:
> just change the regexp as required.

Ok. I decided (although just for game now) to play a little with the
idea of building the regexp.
Starting from Eric's post I slowly progressed to sth. quite similar to
your post :) :

fn buildre {
       re = 's:^([ 	]*)('
       for(i in `{seq 1 `{hoc -e $1-1}})
               re = $re ^ '[^ 	]+[ 	]+'
       re = $re ^ ')[^ 	]+:\1\2' ^ $2:
}

This works (even takes care about leading spaces) unless I want to use
it for the 1st field. Then the produced regexp (buildre 1 hell)is

s:^([ 	]*)()[^ 	]+:\1\2hell:

and sed says
sed: Command garbled: s:^([ 	]*)()[^ 	]+:\1\2hell:

Apparently it dislikes the empty group, (). Is there any reason?
I tried it in linux, there with

echo '1 28	 	3' | sed 's:^\([ 	]*\)\(\)[^ 	][^ 	]*:\1\2hell:'

and it works as expected...

Thanks
Ruda