[ILUG] A little contest

[Fergal Daly]

At 19:27 22/06/00, Fergal Daly wrote:
>At 19:21 22/06/00, Lars Hecking wrote:
>
>>  I was going to post this under "Tip of the day", but then it came
>>  to me that others might enjoy a little food for their brain cells :)
>>
>>  The task: delete every other line in a text file. Naturally, I'm looking
>>  for a scriptable, small, and elegant solution. This probably excludes
>>  Word macros ...
>
>perl -ne 'print if $a; $a = not $a' filename
>
>or if you want the odd line
>
>perl -ne 'print if not $a; $a = not $a' filename

Sorry but I'd hate it if someone else posted these.

perl -ne 'print if ($. % 2)'

which works can be adjusted to print/skip every nth line.

Also, depending on whether you want to skip the first or second line

perl -ne '<>;print' filename

perl -ne 'print;<>' filename

Hmm... just tested those last 2 and they both print only the odds, what's 
going on there?

I don't think this'll be beat

perl -pe '<>' filename

Finally if all this perl is just too much for you

cat -n filename | grep "^ *[0-9]*[24680][[:space:]]" | sed 's/^ 
*[0-9]*[[:space:]]//'

would be a ridiculous but Perl-free way around it,

Fergal