wireshark(1) -k -i -
Interactively dump and analyze network traffic
-k  Start the capture session immediately.  If the -i flag was specified, the capture uses the specified
    interface.  Otherwise, Wireshark searches the list of interfaces, choosing the first non-loopback
    interface if there are any non-loopback interfaces, and choosing the first loopback interface if
    there are no non-loopback interfaces; if there are no interfaces, Wireshark reports an error and
    doesn't start the capture.
-i  <capture interface>|-
    Set the name of the network interface or pipe to use for live packet capture.

    Network interface names should match one of the names listed in "wireshark -D" (described above); a
    number, as reported by "wireshark -D", can also be used.  If you're using UNIX, "netstat -i" or
    "ifconfig -a" might also work to list interface names, although not all versions of UNIX support the
    -a flag to ifconfig.

    If no interface is specified, Wireshark searches the list of interfaces, choosing the first non-
    loopback interface if there are any non-loopback interfaces, and choosing the first loopback
    interface if there are no non-loopback interfaces. If there are no interfaces at all, Wireshark
    reports an error and doesn't start the capture.

    Pipe names should be either the name of a FIFO (named pipe) or ``-'' to read data from the standard
    input. On Windows systems, pipe names must be of the form ``\\pipe\.\pipename''. Data read from pipes
    must be in standard libpcap format.
source manpages: wireshark