unix - Joining two consecutive lines using awk or sed

Question

How would I join two lines using awk or sed?

I have data that looks like this:

abcd
joinabcd
efgh
joinefgh
ijkl
joinijkl

I need an output like the one below:

joinabcdabcd
joinefghefgh
joinijklijkl

Answer 1

awk '!(NR%2){print$0p}{p=$0}' infile