Drupal and debugging often means using Devel, which ships with some
very useful functions like
dpq() and more for outputting debug stuff,
but these sometimes fail to display things on your site due to some reasons (e.g. called too
late, an issue with a template, AJAX…).
Devel ships with a bit more magic that can help though, you can simply use
which “logs a variable to a drupal_debug.txt in the site’s temp directory”, so you can simply
in your code, and then
tail -f /tmp/drupal_debug.txt for live feed
of your debug goodies (or just open the file in an editor like a normal person).
Note: This is more-or-less a last resort help for me, I prefer using breakpoints
in my IDE which is way better and does not require knowing any of this. But I though
dd() was cool as well :-).