nstask output 2 console

main.m

//
//  main.m
//  sandbox-nstask
//
//  Created by Ivan Burlakov on 11/12/15.
//  Copyright © 2015 Ivan Burlakov. All rights reserved.
//

#import <Foundation/Foundation.h>
#import "TaskLauncher.h"

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        
        [[[TaskLauncher alloc] init] start];

        NSLog(@"The End");
    }
    return 0;
}

TaskLauncher.h

//
//  TaskLauncher.h
//  sandbox-nstask
//
//  Created by Ivan Burlakov on 11/12/15.
//  Copyright © 2015 Ivan Burlakov. All rights reserved.
//

#import <Foundation/Foundation.h>

@interface TaskLauncher : NSObject

- (void)start;
@end

TaskLauncher.m

//
//  TaskLauncher.m
//  sandbox-nstask
//
//  Created by Ivan Burlakov on 11/12/15.
//  Copyright © 2015 Ivan Burlakov. All rights reserved.
//

#import "TaskLauncher.h"

@implementation TaskLauncher
- (void)start {

    NSTask *t = [[NSTask alloc] init];
    [t setLaunchPath:@"/bin/echo"];
    [t setArguments:@[@"Hello World!"]];
    
    NSPipe *outputPipe = [NSPipe pipe];
    [t setStandardOutput:outputPipe];
    [t setStandardError:outputPipe];

    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(readCompleted:)
                                                 name:NSFileHandleReadToEndOfFileCompletionNotification
                                               object:[outputPipe fileHandleForReading]];
    [[outputPipe fileHandleForReading] readToEndOfFileInBackgroundAndNotify];

    [t launch];
    [t waitUntilExit];
}

- (void)readCompleted:(NSNotification *)notification {
    NSData *data = [[notification userInfo] objectForKey:NSFileHandleNotificationDataItem];
    NSString *string = [[NSString alloc] initWithData: data
                                             encoding: [NSString defaultCStringEncoding]];

    NSLog(@"OUTPUT/ERROR: %@", string);

    [[NSNotificationCenter defaultCenter] removeObserver:self
                                                    name:NSFileHandleReadToEndOfFileCompletionNotification
                                                  object:[notification object]];
}

@end