2 simple questions but emergent

Hi, friends, I have 3 questions emergent. Please help me.

1.what command for this problem

  I want to creat a newer file called "current"that contains only those records in the new "friends" file that also appear in my older version from last year called "mates". This old file is currently located in the "/home/guest/myfriends".

2.after booting my Linux computer, I am unsure whether the NIC is working correctly, or that it has been correctly configured. show the commands, and a brief explanation for each one, that I would use to verify that the NIC was functioning correctly.Assuem that all operations MUST be carried out from the Linux computer, and that you do not have ready access to another networked workstation.

3. I have correctly installed Linux on a workstation and it works just fine within my subnet. However, it appears that you are unable to access outside the subnet-i.e. I cannot see the Internet. Show what steps you would follow in resolving the problem. assume that ALL cable connections are ok, and that other Linux workstations inside my subnet can see the Internet.