How to extract x lines every y number of lines

Question

I have a big file from which I want to extract x lines every y number of lines. I searched around and found some answers on how to print the first z lines, something like tail -n +<lines to skip + 1> I'm trying to combine it with sed but don't know how.

Answer 1

To print the first two lines of every tex lines, try:

awk -v x=2 -v y=10 '(NR - 1) % y < x'

For example:

$ seq 20 | awk -v x=2 -v y=10 '(NR - 1) % y < x'
1
2
11
12

How it works

Awk reads through the input line-by-line. It will print the line if the condition (NR - 1) % y < x is true. NR is the line number starting at one for the first line.