Run a shell command on Objective c and simultaneously get output

Let's say I want to run curl -o http://example.com/file.zip via an Objective C app and I want to have a label or text box containing the download status which gets updated while the command is running. Maybe this could be achieved using dispatch_async, but now sure how. Before marking as duplicate, the methods I found, run the command, and after it has finished you get the output. I want to get the output while it's running, kinda like a terminal emulator.