NSTask NSPipe - objective c command line help - objective-c

Question

Here is my code:
task = [[NSTask alloc] init];
[task setCurrentDirectoryPath:#"/applications/jarvis/brain/"];
[task setLaunchPath:#"/applications/jarvis/brain/server.sh"];
NSPipe * out = [NSPipe pipe];
[task setStandardOutput:out];
[task launch];
[task waitUntilExit];
[task release];
NSFileHandle * read = [out fileHandleForReading];
NSData * dataRead = [read readDataToEndOfFile];
NSString * stringRead = [[[NSString alloc] initWithData:dataRead encoding:NSUTF8StringEncoding] autorelease];
So I'm trying to replicate this:
cd /applications/jarvis/brain/
./server.sh
but using NSTask in objective-c.
For some reason though, when I run this code, stringRead, returns nothing. It should return what terminal is returning when I launch the .sh file. Correct?
Any ideas?
Elijah

Answer 1

Xcode Bug
There's a bug in Xcode that stops it from printing any output after a a new task using standard output is launched (it collects all output, but no longer prints anything). You're going to have to call [task setStandardInput:[NSPipe pipe]] to get it to show output again (or, alternatively, have the task print to stderr instead of stdout).
Suggestion for final code:
NSTask *server = [NSTask new];
[server setLaunchPath:#"/bin/sh"];
[server setArguments:[NSArray arrayWithObject:#"/path/to/server.sh"]];
[server setCurrentDirectoryPath:#"/path/to/current/directory/"];
NSPipe *outputPipe = [NSPipe pipe];
[server setStandardInput:[NSPipe pipe]];
[server setStandardOutput:outputPipe];
[server launch];
[server waitUntilExit]; // Alternatively, make it asynchronous.
[server release];
NSData *outputData = [[outputPipe fileHandleForReading] readDataToEndOfFile];
NSString *outputString = [[[NSString alloc] initWithData:outputData encoding:NSUTF8StringEncoding] autorelease]; // Autorelease optional, depending on usage.

Answer 2

The solution above is freezing because it's synchronous.
Call to [server waitUntilExit] blocks the run loop until the tasks is done.
Here's the async solution for getting the task output.
task.standardOutput = [NSPipe pipe];
[[task.standardOutput fileHandleForReading] setReadabilityHandler:^(NSFileHandle *file) {
NSData *data = [file availableData]; // this will read to EOF, so call only once
NSLog(#"Task output! %#", [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding]);
// if you're collecting the whole output of a task, you may store it on a property
[self.taskOutput appendData:data];
}];
Probably you want to repeat the same above for task.standardError.
IMPORTANT:
When your task terminates, you have to set readabilityHandler block to nil; otherwise, you'll encounter high CPU usage, as the reading will never stop.
[task setTerminationHandler:^(NSTask *task) {
// do your stuff on completion
[task.standardOutput fileHandleForReading].readabilityHandler = nil;
[task.standardError fileHandleForReading].readabilityHandler = nil;
}];
This is all asynchronous (and you should do it async), so your method should have a ^completion block.