NSTaskの使い方

  NSTask *task = [[NSTask alloc] init];
  task.launchPath = @"/usr/bin/ruby";

  NSArray *arguments = [NSArray arrayWithObjects:@"arg1", @"arg2", nil];
  task.arguments = arguments;
  NSPipe *pipe = [NSPipe pipe];
  task.standardOutput = pipe;
  NSFileHandle *file = [pipe fileHandleForReading];

  [task launch];
  NSData *data = [file readDataToEndOfFile];
  NSString *retval = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];

via http://stackoverflow.com/questions/412562/execute-a-terminal-command-from-a-cocoa-app