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

awk 'BEGIN{i=1}{line[i++]=$0}END{j=1; while (j

No need for sed.