sed find and replace line containing string after IP address

Question

I'm trying to use sed to find a line containing a string after an IP address and replace that line. To illustrate, I have a text file like so ...

192.168.10.155 Mike
8.8.8.8 Googley
123.231.123.3 Tom
192.238.8.10 Matt

Let's say I want to find and replace Tom's line, and I want to match on a Tom AFTER an IP address and a space. Each octet of the IP address could have between 1 and 3 digits. Currently, I have ...

newIpAddress="111.111.111.111"
sed -i "/[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3} Tom/c\$newIpAddress Tom" file

But this doesn't seem to work. Any ideas as to how I could fix that first part to properly match dynamically on any IP address with 1 to 3 digits per octet?

Answer 1

Here is the awk approach:

$ new_ip=1.1.1.1    

$ awk -v ip="$new_ip" '$2=="Tom"{$1=ip}1' file
192.168.10.155 Mike
8.8.8.8 Googley
1.1.1.1 Tom
192.238.8.10 Matt

Answer 2

sed -ri "/[0-9]{1,3}(\.[0-9]{1,3}){3} Tom$/c$newip Tom" file