Objective-c: How to use NSPipe output the illegal command echo in a NSTask?

Question

I have code like following, it's ok, but I have 2 question about it.

1) If I assign some illegal para to sh, for example @"ls - l", then the outString is null. That is to say, it can not capture the error warning "ls: -: No such file or directory ls: l: No such file or directory". How can I deal with it?

2) How can I implement this function: given the app's current directory is "/user/Doc", and I perform sh = @"cd /", then I perform sh = @"ls -l" to see the content under the "/" directory at next loop. But when new loop starts, the current directory resume to "/user/Doc". How can I remain the task environment of last loop?

Furthermore, can I remain a persistent task to run "/bin/sh",just like work on the Terminal directly?

NSString *sh = @"ls -l";
while(sh != @"end"){
    NSTask *shData = [[NSTask alloc] init];
    [shData setLaunchPath: @"/bin/sh"];

    NSArray *args;
    args = [NSArray arrayWithObjects: @"-c", sh, nil];
    [shData setArguments: args];

    NSPipe *myPipe;
    myPipe = [NSPipe pipe];
    [shData setStandardOutput: myPipe];
    [shData setStandardInput:[NSPipe pipe]];

    NSFileHandle *file;
    file = [myPipe fileHandleForReading];

    [shData launch];

    NSData *data1;    
    data1 = [file readDataToEndOfFile];

    NSString *outString;
    outString = [[NSString alloc] initWithData: data1 encoding: NSUTF8StringEncoding];

    NSLog(@"%@",outString);
}

Answer 1

1. That string is on standard error, not standard output. Since you don't check the error stream, you won't find it.

2. That's not how subshells work. Google for "why is cd a shell builtin" for lots of information.