UNIX Command Line

Input file:

$ cat rft01.txt
data set 01
unid=ef023; pid=34
data set 03
data set 09
unid=ef028; pid=36
data set 02
unid=ef021; pid=54

Output Required:
concatenate lines in the above file such that the o/p looks like this:

data set 01 unid=ef023; pid=34
data set 03
data set 09 unid=ef028; pid=36
data set 02 unid=ef021; pid=54

Awk solution:

$ awk 'END{print RS}$0=(/^data set/?NR==1?_:RS:FS)$0' ORS= rft01.txt

data set 01 unid=ef023; pid=34
data set 03
data set 09 unid=ef028; pid=36
data set 02 unid=ef021; pid=54

And if you want the o/p like this:

data set 01 unid=ef023; pid=34
data set 09 unid=ef028; pid=36
data set 02 unid=ef021; pid=54

The awk solution would be:

$ awk '/^data set/{s=$0;next}{print s " "$0}' rft01.txt

Related post:

- Merging lines using awk
- Merge previous line using sed