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

Alternative to sed, awk, grep:

xargs -n2 -d'\n'

This is best when you want to join N lines and you only need space delimited output.

My original answer was xargs -n2 which separates on words rather than lines. -d can be used to split the input by any single character.