parse_hosts.rb

hosts_file = File.readlines('/path/to/hosts')

group_names = []
host_names = []

hosts_file.each do |line|
  line.chomp!

  first_char = line[0]
  last_char = line[-1, 1]
  
  group_names << line if first_char == '[' && last_char == ']'
  host_names << line if line.count('.') >= 1
end

p 'group names:'
p group_names

p 'host names:'
p host_names