$ cat AtoF A B C D E F
Print only odd lines
sed -n 'p;n' AtoF A C E
-n suppress automatic printing of pattern space, p print the current pattern space, n read/append the next line of input into the pattern space.
Alternatively:
$ sed -n 1~2p AtoF A C E
-n suppress automatic printing of pattern space, 1~2 from the 1st line match every line every 2 steps, p print the current pattern space. sed -n 0~p has the same effect . print only the even lines.
Print only even lines
$ sed -n 'n;p' AtoF B D F
or
$ sed -n 2~2p AtoF B D F
0~2p would also work. I prefer