Realtime "capture and echo" command output

[G_M__webkfoe_]

Hi,
I was wondering if I can be able to run a command by script, and while that command is running, capture it's realtime output and print it.

Let's make an example to be more clear:

if I run sysdiagnose, I'll be able to see a progress.

Can I capture that command progress and use it, for example, echoing that progress..?

Hope I am not too confusing and building high castles for nothing..

Thanks everyone!!