[OFF] sed equivalent of something easy in python

[Daniel Fetchinson]

This question is really about sed not python, hence it's totally off.
But since lots of unix heads are frequenting this list I thought I'd
try my luck nevertheless.

If I have a file with content

1
2
3
4
5
6
7
8
.......

i.e. each line contains simply its line number, then it's quite easy
to convert it into

2
3
7
8
12
13
...........

using python. The pattern is that the first line is deleted, then 2
lines are kept, 3 lines are deleted, 2 lines are kept, 3 lines are
deleted, etc, etc.

But I couldn't find a way to do this with sed and since the whole
operation is currently done with a bash script I'd hate to move to
python just to do this simple task.

What would be the sed equivalent?

Cheers,
Daniel



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