How do I see if there's any data available on the serial port?

I'm setting up serial communication between MATLAB and Arduino. At some point in my MATLAB code, I want to look for data on the port. If Arduino has sent '1', MATLAB shoul do some instructions, and else if there is no data, it should just go on with the rest of the code. At first, I used fscanf. But how do I make it so MATLAB doesn't wait for the data to come if there's not any?

Here's that part of the code:

while go
    
    f=fscanf(x,'%u'); %%%***** I want to go to 'i=i+1' if there is no serial data available.
    
    if f==1 %signal for sending parameters
        fprintf(x, p(i));
    end
    
    i=i+1;
    if i>n
        i=1;
    end
        
end

[Walter Roberson]

You should probably rewrite in terms of bytesavailsblefnc callbacks.