NSTask data split by newline \n - objective-c

Question

I'm new to objective-C, so please forgive me if I'm missing something. But we all have to start somewhere :)
I have a snippet of code I got from another open source project that executes a command and passes the result to another method. What I need to do is listen for each new line printed to stdout and do something with each line.
The code snippet I'm working with is the following:
NSMutableArray *args = [NSMutableArray array];
NSString *input = [details valueForKey:#"input"];
for (NSString *i in [input componentsSeparatedByCharactersInSet:[NSCharacterSet whitespaceCharacterSet]]) {
[args addObject:i];
}
NSTask *scriptTask = [NSTask new];
NSPipe *outputPipe = [NSPipe pipe];
if ([_NSFileManager() isExecutableFileAtPath:scriptPath] == NO) {
NSArray *chmodArguments = #[#"+x", scriptPath];
NSTask *chmod = [NSTask launchedTaskWithLaunchPath:#"/bin/chmod" arguments:chmodArguments];
[chmod waitUntilExit];
}
[scriptTask setStandardOutput:outputPipe];
[scriptTask setLaunchPath:scriptPath];
[scriptTask setArguments:args];
NSFileHandle *filehandle = [outputPipe fileHandleForReading];
[scriptTask launch];
[scriptTask waitUntilExit];
NSData *outputData = [filehandle readDataToEndOfFile];
NSString *outputString = [NSString stringWithData:outputData encoding:NSUTF8StringEncoding];
if (NSObjectIsNotEmpty(outputString)) {
[self.world.iomt inputText:outputString command:IRCPrivateCommandIndex("privmsg")];
}
So, rather than waiting for the process to complete then doing something with the result, I need to wait for each new line that gets printed by the command to stdout.
My background is mostly in web dev, so I guess if you were using Node.js and event emitters my aim would look similar to the following:
task = new Task("ls");
task.addListener("newline", function(data) {
somethingElse("sendmsg", data);
});
task.run();
Hopefully you understand what I'm tying to achieve. Thanks!

Answer 1

What you can do is add an observer to the NSFileHandle to notify you when it reads something.
example:
[fileHandler readInBackgroundAndNotify];
//Need to set NSTask output pipes
[self.task setStandardOutput: outputPipe];
[self.task setStandardError: outputPipe];
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(readFromTask:) name:NSFileHandleReadCompletionNotification object:fileHandler];
-(void)readFromTask:(NSNotification *)aNotifcation;
{
NSData *data = [[aNotifcation userInfo] objectForKey: NSFileHandleNotificationDataItem];
if (data != 0) {
NSString *text = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
// Do something with the text
[text release];
[[aNotifcation object] readInBackgroundAndNotify];
}
}
Then there's a notififcation you can add to the task to indicate when its completed so you can do clean up.
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(taskEnded:) name:NSTaskDidTerminateNotification object:task];
- (void)taskEnded:(NSNotification *) aNotifcation
{
NSData *data = [[aNotifcation userInfo] objectForKey: NSFileHandleNotificationDataItem];
if (data != 0) {
NSString *text = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
[text release];
}
[self.task release];
}
So from your code, you could remove:
[scriptTask waitUntilExit];
And move the data handling into the notifications.
NSData *outputData = [filehandle readDataToEndOfFile];
NSString *outputString = [NSString stringWithData:outputData encoding:NSUTF8StringEncoding];
if (NSObjectIsNotEmpty(outputString)) {
[self.world.iomt inputText:outputString command:IRCPrivateCommandIndex("privmsg")];
}
That's a rough idea, there's a good post at
http://www.cocoabuilder.com/archive/cocoa/306145-nstask-oddity-with-getting-stdout.html