Joining two consecutive lines awk sed

Question

How would i join two lines usung awk or sed?

for eg:

i have data like below:

abcd
joinabcd
efgh
joinefgh
ijkl
joinijkl

i need oupput like below:

joinabcdabcd
joinefghefgh
joinijklijkl

Answer 1

awk 'BEGIN{i=1}{line[i++]=$0}END{j=1; while (j<i) {print line[j+1] line[j]; j+=2}}' yourfile

No need for sed.

Answer 2

Here it is in sed:

sed 'h;s/.*//;N;G;s/\n//g' < filename

Answer 3

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