The Beanstalk The Beanstalk - 1 year ago 215
Swift Question

Real time NSTask output to NSTextView with Swift

I'm using an NSTask to run rsync, and I'd like the status to show up in the text view of a scroll view inside a window. Right now I have this:

let pipe = NSPipe()
task2.standardOutput = pipe

let data = pipe.fileHandleForReading.readDataToEndOfFile()
let output: String = NSString(data: data, encoding: NSASCIIStringEncoding)! as String

textView.string = output

And that get's me the some of the statistics about the transfer, but I'd like to get the output in real time, like what get's printed out when I run the app in Xcode, and put it into the text view. Is there a way to do this?

Answer Source

You can read asynchronously from a pipe, using notifications. Here is a simple example demonstrating how it works, hopefully that helps you to get started:

let task = NSTask()
task.launchPath = "/bin/sh"
task.arguments = ["-c", "echo 1 ; sleep 1 ; echo 2 ; sleep 1 ; echo 3 ; sleep 1 ; echo 4"]

let pipe = NSPipe()
task.standardOutput = pipe
let outHandle = pipe.fileHandleForReading

var obs1 : NSObjectProtocol!
obs1 = NSNotificationCenter.defaultCenter().addObserverForName(NSFileHandleDataAvailableNotification,
    object: outHandle, queue: nil) {  notification -> Void in
        let data = outHandle.availableData
        if data.length > 0 {
            if let str = NSString(data: data, encoding: NSUTF8StringEncoding) {
                print("got output: \(str)")
        } else {
            print("EOF on stdout from process")

var obs2 : NSObjectProtocol!
obs2 = NSNotificationCenter.defaultCenter().addObserverForName(NSTaskDidTerminateNotification,
    object: task, queue: nil) { notification -> Void in


Instead of print("got output: \(str)") you can append the received string to your text view.

The above code assumes that a runloop is active (which is the case in a default Cocoa application).