ShellScript.h

//
//  ShellScript.h
//
//  Created by Koki Ibukuro on 6/18/14.
//  Copyright (c) 2014 Koki Ibukuro. All rights reserved.
//

#import <Foundation/Foundation.h>

typedef void (^ShellScriptMessageCallback)(NSString* msg);

@interface ShellScript : NSObject

// class methods
+ (NSString*) doScript:(NSString*)script directory:(NSString*)directory;

// methods
- (void) runScriptAsync:(NSString*)script directory:(NSString*)directory;
- (void) stopScript;

// property
@property (strong, nonatomic) ShellScriptMessageCallback onMessage;

@end

ShellScript.m

//
//  ShellScript.m
//
//  Created by Koki Ibukuro on 6/18/14.
//  Copyright (c) 2014 Koki Ibukuro. All rights reserved.
//

#import "ShellScript.h"

@interface ShellScript() {
    NSTask *_task;
}
@end

@implementation ShellScript

#pragma mark -
#pragma mark Methods

- (id) init {
    if(self == [super self]) {
    }
    return self;
}

- (void) dealloc {
    [self stopScript];
}

- (void) runScriptAsync:(NSString *)script directory:(NSString*)directory {
    _task = [ShellScript createShellTask:script];
    if(directory) {
        [_task setCurrentDirectoryPath:directory];
    }
    NSPipe *out_pipe = [NSPipe pipe];
    [_task setStandardOutput:out_pipe];
    
    NSNotificationCenter * notificationCenter = [NSNotificationCenter defaultCenter];
    [notificationCenter addObserver:self selector:@selector(onReadData:) name:NSFileHandleReadCompletionNotification object:[out_pipe fileHandleForReading]];
    [notificationCenter addObserver:self selector:@selector(onTerminate:) name:NSTaskDidTerminateNotification object:nil];
    
    [[out_pipe fileHandleForReading] readInBackgroundAndNotify];
    
    [_task launch];
}

- (void) stopScript {
    [_task terminate];
    
    NSNotificationCenter * notificationCenter = [NSNotificationCenter defaultCenter];
    [notificationCenter removeObserver:self name:NSFileHandleReadCompletionNotification object:nil];
    [notificationCenter removeObserver:self name:NSTaskDidTerminateNotification object:nil];
}

- (void) onReadData:(NSNotification*)notification {
    NSData *data = [[notification userInfo] objectForKey:NSFileHandleNotificationDataItem];
    if(data != nil && [data length]) {
        NSString* msg = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
        if(self.onMessage) {
            self.onMessage(msg);
        }
        [[notification object] readInBackgroundAndNotify];
    }
    else {
        [self stopScript];
    }
}

- (void) onTerminate:(NSNotification*)notification {
    [self stopScript];
}

#pragma mark -
#pragma mark Static

+ (NSTask*) createShellTask:(NSString*) script {
    NSTask* task = [[NSTask alloc] init];
    [task setLaunchPath:@"/bin/bash"];
    [task setArguments:@[@"-c", script]];
    return task;
}

+ (NSString*) doScript:(NSString *)script directory:(NSString*)directory {
    
    NSTask *task = [ShellScript createShellTask:script];
    NSPipe *out_pipe = [NSPipe pipe];
    [task setStandardOutput:out_pipe];
    if(directory) {
        [task setCurrentDirectoryPath:directory];
    }
    
    [task launch];
    
    NSData* data = [[out_pipe fileHandleForReading] readDataToEndOfFile];
    return [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
}


@end

Usage.swift

//-----------
// Simple
let result = ShellScript.doScript("ls -l", directory: NSHomeDirectory())
println(result)

//-----------
// Async
func onMessage(msg:String!) {
  print("get message", msg)
}

let shell:ShellScript = ShellScript()
let path = NSHomeDirectory()

shell.runScriptAsync("python -m SimpleHTTPServer 8888", directory:path);

shell.stopScript()