Ever wanted to write each file to standard output (stdout) but with line numbers added?
nl command to the rescue.
1 127.0.0.1 localhost 2 127.0.1.1 test 3 # The following lines are desirable for IPv6 capable hosts 4 ::1 localhost ip6-localhost ip6-loopback 5 ff02::1 ip6-allnodes 6 ff02::2 ip6-allrouters
nl stands for number lines. Review its man page to learn more. This can be achieved with many other commands too, but this one is the simplest I have ever seen in my sysadmin career. And it's always good to keep things simple, right? :)