How to merge every two lines into one from the command line?

Question

I have a text file with the following format. The first line is the \"KEY\" and the second line is the \"VALUE\".

KEY 4048:1736 string
3
KEY 0:1772 string
1         


        

Answer 1

Simplest way is here:

1. Remove even lines and write it in some temp file 1.
2. Remove odd lines and write it in some temp file 2.
3. Combine two files in one by using paste command with -d (means delete space)

sed '0~2d' file > 1 && sed '1~2d' file > 2 && paste -d " " 1 2