iPhone SDK: System() questions

Question

I got bored earlier and wondered if you could execute terminal commands on the iOS platform. Surely enough, just like OSX you can. This is really awesome, but how do I output what the terminal outputs to a text area or something similar? It's nothing serious, just a fun project.
I am using system("") to do it.

Answer 1

This, my friend is one of the downsides to using system. I also hope you understand that system is unavailable on a non-jailbroken iDevice, so unless you are installing it as instructed on the #1 answer on iPhone App Minus App Store, then you can't use it.

Now, moving forward, you have a few options.

1. Pipe the output of the command to a file, and read that file in your application. Your code should look something like this:

   system("myCommand -f \"/path/to/my/file\" > output.txt")
   
   NSString *results = [NSString stringWithContentsOfFile:@"output.txt" usedEncoding:nil error:nil];
   NSLog(@"%@", results);
   

2. Create the process with the popen function, and then pipe the output directly into your application:

   NSFileHandle *openProcessRead(const char *command)
   {
       FILE *fPtr = popen(command, "r");
   
       NSFileHandle *fileHandle = [[NSFileHandle alloc] initWithFileDescriptor:fileno(fPtr) closeOnDealloc:YES];
   
       return fileHandle;
   }
   

   You can now use the NSFileHandle docs to do what you need.