Shell Programming and Scripting

Ok. I went with Franklin's awk solution and it works beautifully.
I also expanded it to include a third column named alias and also modified the code in such a way that it understands the space separated fields of the alias line.

define host{
host_name HostA
alias Also Known As Host A
parents HostNull
}
--
define host{
host_name HostB
alias Also Known As Host B
parents HostA
}

awk 'BEGIN {print "host,alias,parent"}
/host_name/{p=$2;printf p",";getline;
pi=NF;for (i=2;i<pi+1;i++) printf $i" ";getline;
p3=$2;print "\b,"p3}
' source.txt

host,alias,parent
HostA,Also Known As Host A,HostNull
HostB,Also Known As Host B,HostA

Thanks again. This is just what i needed.