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

Although it seems the previous solutions would work, if a single anomaly occurs in the document the output would go to pieces. Below is a bit safer.

sed -n '/KEY/{
N
s/\n/ /p
}' somefile.txt