android : how to run a shell command from within code

The phone needs to be rooted, afterwards you can do something like:

public static void doCmds(List<String> cmds) throws Exception {
    Process process = Runtime.getRuntime().exec("su");
    DataOutputStream os = new DataOutputStream(process.getOutputStream());

    for (String tmpCmd : cmds) {
            os.writeBytes(tmpCmd+"\n");
    }

    os.writeBytes("exit\n");
    os.flush();
    os.close();

    process.waitFor();
}    

If you're just trying to set brightness, why don't you do so through the provided API (AKA, is there a reason you are trying to do it the way you are).

int brightness = 125; 
Settings.System.putInt(
      ftaContext.getContentResolver(), 
      Settings.System.SCREEN_BRIGHTNESS, 
      brightness); 

Agreed you probably need to root the phone to write to system files. I'm surprised the brightness isn't exposed through the SDK.

For details on running shell commands from code, check out this project:

You also may remout /system with permissions to write..

I think the device will need to be "rooted" for this to work. Have a search on google and see how other developers have dont this, there is no shortage of flashlight apps.

The adb shell can behave as a superuser without rooted devices. it's a debug bridge. you can do whatever you want through it.

BUT, when your calling Runtime.getRuntime().exec, you don't have the same premissions. some shell commands aren't even available from exec.

so not only you need a rooted device, you also need su premmisions.