str =<<DATA
[example.com]
10.100.251.1
10.100.251.2
10.100.251.3
[example.net]
10.100.251.22
10.100.251.33
DATA
rx = /^\[example\.com\]\R*(?:(?:\d{1,3}\.){3}\d{1,3}\R*)*/
puts str[rx]