If you want to generate a hosts file with OpenStack nova, this little gem should set you straight. The last little bit pulls out any instances which don't have a private IP. In this case, we're assuming that our subnet begins with '10'. Feel free to change for whatever else you like.

gistfile1.sh

$ nova list | awk 'BEGIN {FS="[|=,]"}  {gsub(/[[:space:]]+/,"",$3);gsub(/[[:space:]]+/,"",$6);  print $6" "$3}' | tail -n +3 | grep 10

10.1.1.141 Server2592
10.1.1.136 Server2598
10.1.1.140 Server2599
10.1.1.138 Server2600
10.1.1.143 Server2601
10.1.1.147 Server2602