Printing logcat for only my package name on file?

Question

In my android app, I am writing to file the whole logcat like this:

Runtime.getRuntime().exec( "logcat -f " + dir +"Log"+System.currentTimeMillis()+".txt");

but I would like to filter out just the output of my app's package name. I've tried with grep but that didn't help me. There is no built-in way to filer out lines?

Thank you.