How to get total size of folders with find and du?
Use xargs(1) instead of -exec:
find . -name bak -type d | xargs du -ch-exec executes the command for each file found (check the find(1) documentation). Piping to xargs lets you aggregate those filenames and only run du once. You could also do:
find -name bak -type d -exec du -ch '{}' \; +If your version of find supports it.
If there are many files, using -exec ... + may be executed multiple times and you would get multiple subtotals.
An alternative is to pipe the result of find:
find . -name bak -type d -print0 | du -ch --files0-from=-