How to selectively save standard err messages / skip progress bars

One way is look for the flags of the program you use, there should have a quiet version.
If it doesn't work, you could do this:

$ find . -name "my.txt" 2>&1 | grep -v "Permission denied"

The above command will suppress only "Permission denied" warning message, and show any other warning or error messages unfiltered.

reference: 

http://xmodulo.com/how-to-suppress-warning-or-error-messages-in-find-command.html