I need to remove every second and every third line from a file. My idea was to do it in two operations. First every third line, then every second line. The problem is that i can't find out how to do it. I tried to look for some sed oneliners, but couldn't find any.

Suggestions?

awk 'NR%3 != 0' filename

in the same way, change 3 as 2 to remove 2nd line from the file

Is this what you mean?

$ cat bistru.txt
line 1
line 2
line 3
line 4
line 5
line 6
line 7
line 8
line 9
$ sed -n 'p;N;N' bistru.txt
line 1
line 4
line 7
$

Thanks, both worked perfectly!

BTW, zazzybob, i'm not able to understand the syntax rather well. Do You mind giving a short explanation? I understand '-n' and that 'p' overruns the '-n'. From man sed i found that 'n' or 'N' means that the next line is input into the pattern space, implying that the line is suppressed. Am i completely wrong here, or?

in one shot it can be done,

awk 'NR % 3 == 1' filename