Find number of connection(tmsh command)

A Virtual IP (VIP) is an IP address that is used for one or more Virtual Servers (VSs). A VS, in turn, is the combination of an IP address (or netblock) and a port (or the wildcard port). I make the distinction here because the answer to your question is slightly (though only slightly) different depending on whether you mean a VIP or a VS. I'm going to assume you mean a VS.

There are two different ways you can get an answer to your question from tmsh. The first is to look at the VS statistics:

 tmsh show ltm virtual vs-web-01

------------------------------------------------------------------
Ltm::Virtual Server: vs-web-01 
------------------------------------------------------------------
Status                         
  Availability     : online   
  State            : enabled   
  Reason           : The virtual server is up
  CMP              : enabled   
  CMP Mode         : all-cpus  
  Destination      : 78.61.50.1:80
                               
Traffic                             ClientSide  Ephemeral  General
  Bits In                                 3.6G          0        -
  Bits Out                                3.2G          0        -
  Packets In                              478M          0        -
  Packets Out                             398M          0        -
  Current Connections                        0          0        -
  Maximum Connections                     2.4K          0        -
  Total Connections                      15.5M          0        -
  Min Conn Duration/msec                     -          -        0
  Max Conn Duration/msec                     -          -        0
  Mean Conn Duration/msec                    -          -        0
  Total Requests                             -          -        0
                               
SYN Cookies                    
  Status                         not-activated
  Hardware SYN Cookie Instances              0
  Software SYN Cookie Instances              0
  Current SYN Cache                          0
  SYN Cache Overflow                         0
  Total Software                             0
  Total Software Accepted                    0
  Total Software Rejected                    0
  Total Hardware                             0
  Total Hardware Accepted                    0
                               
CPU Usage Ratio (%)            
  Last 5 Seconds                             0
  Last 1 Minute                              5
  Last 5 Minutes                            22

Alternatively, you can see a snapshot of current connections by dumping part of the connection table with a selector:

 tmsh show sys connection cs-server-addr 78.61.50.1 cs-server-port 80

There is already a DevCentral article that describes the output of this tmsh command in great detail.

For the record, if you really do want to see information about a Virtual IP, that is also possible:

 tmsh show ltm virtual-ip 78.61.50.1

or

 tmsh show sys connection cs-server-addr 78.61.50.1