Ruby 正規表現の足し算

irb(main):003:0> ipaddr=/[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}/
=> /[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}/
irb(main):004:0> x=/local\s+IP\s+address\s+/
=> /local\s+IP\s+address\s+/
irb(main):014:0> "local IP address 192.168.211.114".scan(ipaddr)
=> ["192.168.211.114"]
irb(main):015:0> "local IP address 192.168.211.114".scan(x)
=> ["local IP address "]
irb(main):016:0> "local IP address 192.168.211.114".scan(/#{x}#{ipaddr}/)
=> ["local IP address 192.168.211.114"]
irb(main):017:0> "local IP address 192.168.211.114".scan(/#{x}(#{ipaddr})/)
=> "192.168.211.114"