Extracting unnamed fields from PCAP using tshark

Extracting unnamed fields from PCAP using tshark

I'm trying to extract data from PCAPs in order to determine who the user was during the session and / or the host name of the computer.
Most of the time I just do a string search in the packet details for some of the fields listed at the bottom. I tinkered a little with:
tshark -r data.pcap -T fields -e bittorrent.info_hash
and it gave the results, but a lot of empty fields as well.
Two questions. First, how do I tell tshark to only give me output on fields that have data present.
Second, how do I tell it to grep for some of the following examples?
==========
To find the Host Name I do a string search in the packet details for the following:
Host Name:
Host=
NetBIOSName
HostAddress
Server Name (Service and Host): host/[hostname].
NetBIOS Host
DnsDomain
To find the user name I do a string search in the packet details for the following:
Client Name (Principal)
User name:
COOKIE_last_login=
CN=
Filename:
Any help would be greatly appreciated :)