Sample code to use NSTask(Process) and NSPipe and NSRunloop

NSTaskExample.swift

import Foundation

let task = Process()
// Set the launch tool path
task.launchPath = "/bin/sh"

// Set the command to run the task
let commandStr = "ls -l /Users/derek/PG"// "last | grep reboot"
var arguments = ["-c"]
arguments.append(commandStr)
task.arguments = arguments

// Set up the pipe to read the output data
let pipe = Pipe()
task.standardOutput = pipe
let fileHandle = pipe.fileHandleForReading

// Init a runloop flag to stop the current runloop
var passTheRunloop = false

// Register a notification to read the output data from the pipe
NotificationCenter.default.addObserver(forName: FileHandle.readCompletionNotification,
                                       object: nil,
                                       queue: .current) { notification in
    let data = notification.userInfo?[NSFileHandleNotificationDataItem] as? Data ?? Data()
    let log = String(data: data, encoding: .utf8)
    print("\(log ?? "")")
    
    // Terminate the runloop
    passTheRunloop = true
}

do {
    // Start the task
    try task.run()
    // Read the data output in the background for the reading file handle
    fileHandle.readInBackgroundAndNotify()
} catch {
    print("[DEBUG] Cannot process ls task for directory, /Users/derek/PG")
}

// Start the runloop and run until reaching the termination condition.
let runloop = RunLoop.current

while !passTheRunloop {
    runloop.run(mode: .default, before: Date(timeInterval: 0.1, since: .now))
}

print("[DEBUG] Programm exists!")