to add to this, if you've coded one-liner first, you can convert to script using -o option

for ex:

    awk -o '{ORS = NR%2 ? " " : RS} 1'

gives (default output file is awkprof.out)

    {
        ORS = (NR % 2 ? " " : RS)
    }

    1 {
        print $0
    }