Re: cut off last lines of a document

On Fri, Sep 01, 2023 at 10:43:46AM +0200, Ede Wolf wrote:
> Hello,
> 
> From a file/output with an unknown amount of lines, I would like to filter
> out, or not display, the last 3 lines. Is there a way to archive this?
> 
> For those also using linux, there is a "head -n -3" for this. That negative
> number option is not available on FreeBSD, but maybe there is an alterative
> way of doing this? Preferably /bin/sh compatible.
> 
> Thanks
> 
> Ede

Using awk:

awk -v n=3 'NR > n { print buffer[NR%n] } { buffer[NR%n] = $0 }'

This will print all lines except the last "n" lines.  The buffer array
is a circular buffer that contains the most recently read "n" lines.
The code outputs nothing until the first "n" lines have been read, then
it outputs lines from the buffer array in a circular fashion while at
the same time filling the array with new lines from the input.


-- 
Andreas (Kusalananda) Kähäri
SciLifeLab, NBIS, ICM
Uppsala University, Sweden

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