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Re: Proposed new feature: head --show-truncation

From: Stepan Kasal
Subject: Re: Proposed new feature: head --show-truncation
Date: Thu, 21 Aug 2003 14:29:14 +0200
User-agent: Mutt/


On Thu, Aug 21, 2003 at 12:55:30PM +0100, Ed Avis wrote:
> I can't get this command to work:
> Label too long: 2!b;n;s/.*/[[trunc]]/;q

I apologize; the following versions should be more portable:
        sed -e '2!b' -e 'n;s/.*/[[trunc]]/;q'
        sed -e '2{' -e 'n;s/.*/[[trunc]]/;q;}'
        sed '1,2p;1,2d;s/.*/[[trunc]]/;q'
> >I mean that trivial shell script which doesn't use "head" should
> >also count.
> No, because by that argument at least half of the classic Unix
> utilities would be eliminated.

They are "clasic" because they were born in times when they were
significantly quicker then their shell counterparts.
(Perl was just a jewel with a typo in those times.)

> I am hoping to consider whether the
> --show-truncation flag makes head more powerful, in that it couldn't
> be emulated by the existing head plus a couple of lines of
> shell.

Well, here is one script

n1=`expr $n + 1`
head -n $n1 | sed $n1's/.*/[[trunc]]/'

and here is another:

head -n $n ; sed 's/.*/[[trunc]]/;q'

The later one works only if the input is seekable.
In other words, POSIX doesn't guarantee that it'll work with input
from a pipe, for example.


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