How to read and write to NSTask

Question

I have it working. However, initially it appears to be waiting for input. How can I read what was output before it stops and is waiting for input?

task starts
stdout should post data for "sftp> " but nothing happens, its waiting for input
If I write "\n" to stdin
stdout notifies me of data available which ends up being "sftp> \n"

Here is how it's implemented:

[self.task = [[NSTask alloc] init];
[self.task setLaunchPath:executablePath];
[self.task setArguments: args];

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(terminatedNotification:) name:NSTaskDidTerminateNotification object:self.task];

//reading
self.stdoutPipe = [NSPipe pipe];
self.task.standardOutput = self.stdoutPipe;
[self.stdoutPipe.fileHandleForReading waitForDataInBackgroundAndNotify];

//error
self.stderrorPipe = [NSPipe pipe];
self.task.standardError = self.stderrorPipe;
[self.stderrorPipe.fileHandleForReading waitForDataInBackgroundAndNotify];

/*
reading works perfect until I uncomment this section
//writing
self.stdinPipe = [NSPipe pipe];
self.task.standardInput = self.stdinPipe;
*/

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(dataAvailable:) name:NSFileHandleDataAvailableNotification object:self.stdoutPipe.fileHandleForReading];
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(dataAvailable:) name:NSFileHandleDataAvailableNotification object:self.stderrorPipe.fileHandleForReading];

Answer 1

Data written to a NSFileHandle is buffered. Only after the buffer has been flushed it will be available for reading on the other end of the pipe. The buffer is flushed if

1. it is full and no more data would fit into it.
2. a newline character ("\n") is written to it (autoflush).
3. you flush it explicitly by calling - (void)synchronizeFile