One of the big problems with render arrays is that there are often a bunch of read-only copies of the information that you're looking for. If you want to actually change the render output, you have to find the right one. I usually use dpm(), and then view page source and search through the output there, flipping back and forth between the two displays until I find what I need.
If you want to dump the contents of a render array for a given path to the terminal (e.g. to pass it through grep), you could do something like this:
drush ev '$router_item=menu_get_item("node/7"); require_once(DRUPAL_ROOT .
"/" . $router_item["include_file"]);
You could also just 'view page source' in your browser and use the clipboard, of course, but the above might be the start of a Drush command to view render arrays.
Update: I found a really good article on this subject: The Scary Render Array -- probably the best treatment of render arrays I have seen so far. I should have also mentioned the devel_themer module upfront; it does a good job at "zooming in" on the section of the render array you are interested in.