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From: =?utf-8?Q?Dag-Erling_Sm=C3=B8rgrav?= <des@FreeBSD.org>
To: Ede Wolf <listac@nebelschwaden.de>
Cc: questions@freebsd.org
Subject: Re: cut off last lines of a document
In-Reply-To: <a9b64c1d-02a6-45c1-aaed-85e4cf622776@nebelschwaden.de> (Ede
	Wolf's message of "Mon, 4 Sep 2023 08:53:58 +0200")
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Date: Mon, 04 Sep 2023 16:39:25 +0200
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Ede Wolf <listac@nebelschwaden.de> writes:
> Am 03.09.23 um 23:16 schrieb paul beard:
> > export COUNT=3D`wc -l /var/log/messages | tr -d -c '\n[:digit:]'` #
> > export WANT=3D`echo "$COUNT-3" | bc ` # subtract 3 (or however many)
> > head -$WANT /var/log/messages # display the remainder.

1) there is no need to export the variables
2) don't use backticks, use $() instead
3) if you use 'wc -l <foo' instead of 'wc -l foo' you don't need tr
3b) alternatively, use read: wc -l foo | read COUNT FILENAME
4) the shell can do the math for you: 'head -$((COUNT-3)) foo'

> Thanks, but the problem I currently see here, as with the suggestion
> of Archimedes earlier, I am currently not easily able to convert this
> into a feed from stdin.

Pipe-friendly pure shell solution:

drop_last_three() {
        local a b c d
        read a
        read b
        read c
        while read d ; do
                echo "$a"
                a=3D"$b"
                b=3D"$c"
                c=3D"$d"
        done
}

DES
--=20
Dag-Erling Sm=C3=B8rgrav - des@FreeBSD.org