The handle to a selected signal can be obtained using the 'find_system' command:
>> h_line = find_system(gcs,'FindAll','on','FollowLinks','on','type','line','Selected', 'on');
The names of the source and destination blocks with respect to the selected signal can be obtained using the 'get_param' command with the 'SrcBlockHandle' and 'DstBlockHandle' parameters:
>> source_block_handle = get_param(h_line, 'SrcBlockHandle');
>> source_block_name = get_param(source_block_handle, 'Name');
Similarly, the 'SrcPortHandle' and 'DstPortHandle' parameters can be used to obtain the port numbers associated with the selected signal:
>> source_port_handle = get_param(h_line, 'SrcPortHandle');
>> source_port_number = get_param(source_port_handle, 'PortNumber');
