Shell Programming and Scripting

I am trying to perform the following action.
1. A script runs the 'last' command for some users and prints the output to a file.
$ cat last_users.log
oracle pts/17 10.120.xxx.xxx Jun 28 14:42 - 18:01 (03:19)
oracle pts/11 10.120.xxx.xxx Jun 28 14:28 - 20:17 (5+05:49)
oracle pts/9 10.120.xxx.xxx Jun 28 00:11 - 14:02 (1+13:51)
oracle pts/13 10.120.xxx.xxx Jun 27 14:20 - 14:51 (7+00:31)
oracle pts/5 10.120.xxx.xx May 17 02:16 - 22:48 (5+20:32)
oracle pts/4 10.120.xxx.xx May 16 12:08 - 11:00 (2+22:52)

2. I have a file with some IPs and users associated with the IPs stored.
$ cat ip_list
10.120.xxx.xxx userA
10.120.xxx.xxx userB
10.120.xxx.xxx userC

3. I have to get the IP address from last_users.log, check if it exists in ip_list and get the username. The final output should be something like this

oracle pts/4 10.120.xxx.xx May 16 12:08 - 11:00 (2+22:52) userA

i.e. the username from ip_list should be merged with the last_users.log into a new file.

Thanks

Code:

awk 'NR == FNR {a[$1] = $2; next}
  {$(NF+1) = a[$3]}1' ip_list last_users.log

Thanks a lot ! It works...