Question

I need help to build a regex that can remove EVEN lines in a plain textfile.

Given this input:

line1
line2
line3
line4
line5
line6

It would output this:

line1
line3
line5

Thanks !

Answer 1

Actually, you don’t use regex for that. With your favourite language, iterate the file, use a counter and do modulus. eg with awk (*nix)

$ awk 'NR%2==1' file
line1
line3
line5

even lines:

$ awk 'NR%2==0' file
line2
line4
line6