NSTask/NSPipe read from Unix command

Question

I am writing a Cocoa application which needs to execute a UNIX program and read its output, line by line, as they are produced. I set up a NSTask and NSPipe as such: ``` task = [[NSTask alloc] init]; pipe = [NSPipe pipe]; [task setStandardOutput:pipe]; //... later ... [task setArguments:...]; [task setLaunchPath:@"..."]; [task launch]; handle = [[task fileHandleForReading] retain]; ``` The command does not terminate until the program tells it to do so with `[task terminate]`. I have tried several methods of reading from the handle, such as `-readInBackgroundAndNotify`, `while([(data = [handle availableData]) length] > 0)`, and `-waitForDataInBackgroundAndNotify`, but the pipe never seems to yield any data. Is there some way I can "poke" the `NSTask` or `NSPipe` to flush the data through? EDIT: with `-readInBackgroundAndNotify`: ``` [handle readInBackgroundAndNotify]; notification_block_t handlerBlock = ^(NSNotification *notification) { NSData *data = [[notification userInfo] objectFor…

Accepted Answer

Here is a working example of how I usually do it:

```
    task = [[NSTask alloc] init];
    [task setLaunchPath:...];
    NSArray *arguments;
    arguments = ...;
    [task setArguments:arguments];

NSPipe *outPipe;
    outPipe = [NSPipe pipe];
    [task setStandardOutput:outPipe];

outFile = [outPipe fileHandleForReading];
    [outFile waitForDataInBackgroundAndNotify];
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(commandNotification:)
                                                 name:NSFileHandleDataAvailableNotification 
                                               object:nil];

[task launch];

- (void)commandNotification:(NSNotification *)notification
{
    NSData *data = nil;
    while ((data = [self.outFile availableData]) && [data length]){
        ...
    }   
}
```

NSTask/NSPipe read from Unix command

Solution

Problem