Joining two consecutive lines using awk or sed

Question

How would I join two lines using awk or sed?

for e.g.:

I have data that looks like this:

abcd
joinabcd
efgh
joinefgh
ijkl
j         


        

Answer 1

Some improvement to the "sed" script above that will take the following: 1008
-2734406.132904 2846
-2734414.838455 4636
-2734413.594009 6456
-2734417.316269 8276
-2734414.779617

  and make it :    

1008 -2734406.132904
2846 -2734414.838455
4636 -2734413.594009
6456 -2734417.316269
8276 -2734414.779617

  the "sed" is : "sed 'h;s/.*//;G;N;s/\n/ /g'"