Cocoa shell command permission

I'm developing my first Mac App have some issues with shell commands... I'm trying to find out how to get the permission windows that the user can enter his password. I want to copy a picture in a system folder, and change the name of another picture too. I try to change the Login window background.

Command 1: "sudo mv DefaultDesktop.jpg DefaultDesktop_copy.jpg"

Command 2: "sudo cp /path/of/image.jpg DefaultDesktop.jpg"

With the terminal, it is very easy. But with an interface, i would like this prompt asking for the password.

Here is my code for the first command:

- (void)copyDefaultBackground:(id)sender {
    NSTask *task;
    task = [[NSTask alloc] init];
    [task setLaunchPath: @"/usr/bin/sudo"];

    NSArray *arguments;
    arguments = [NSArray arrayWithObjects:@"mv"
                            @"/System/Library/CoreServices/DefaultDesktop.jpg",
                            @"/System/Library/CoreServices/DefaultDesktop_copy.jpg", 
                            nil];
    [task setArguments: arguments];

    NSPipe *pipe;
  开发者_运维技巧  pipe = [NSPipe pipe];
    [task setStandardOutput: pipe];

    NSFileHandle *file;
    file = [pipe fileHandleForReading];

    [task launch];

    NSData *data;
    data = [file readDataToEndOfFile];

    NSString *string;
    string = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
    NSLog (@"Script returned:\n%@", string);
}

Update:

I found that NSFileManager is an object that allow to manage file on the disk. Isn't it better than using a NSTask with a shell command?

Thank you.

You will need to use Authorization Services to authorize the move:

Introduction to Authorization Services Programming Guide

For the file move itself, why not use NSFileManager? Authorization aside, both your steps (make a backup, then move the new file into place) can be done with a single line of code each with NSFileManager.

What you want is STPrivilegedTask, which is an NSTask-like class which abstracts Authorization Services.

Get rid of sudo and execute the command using STPrivilegedTask -- the user will be prompted for an admin password, and your command will be executed with admin privileges.