Perhaps like this?

knoppix@Microknoppix:~$ perl -E '
> $input = <<EOI;
> 2: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast
+ state UP qlen 1000 link/ether 00:0c:29:4e:97:a1 brd ff:ff:ff:ff:ff:f
+f
> EOI
> 
> $eth = ( split m{\s*:\s*}, $input )[ 1 ];
> say qq{->$eth<-};'
->eth1<-
knoppix@Microknoppix:~$
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