Bash – How to show distinct directories on find

Portably:

find . -type d -exec sh -c 'printf "%s/\n" "$0"' {} \; -or -print

If you're willing to list directories and files separately (you can merge the output by sorting):

{ find . -type d -print | sed 's!$!/!'; find . \! -type d; } | sort

With GNU find, see Shawn J. Goff's answer.

If you're willing to risk non-printable characters being mangled even when not outputting to a terminal, see ddeimeke's answer.

In zsh: print -rl -- **/*(DM) (D to include dot files, M to add a / after directories)

(Your question is not clear: if a directory contains some.foo and some.bar, should it be deleted? I interpreted it as requiring such a directory to be kept.)

The following script should work, provided that no file name contains a newline and no directory matches *.foo. The principle is to traverse the directory from the leaves up (-depth), and as *.foo files are encountered, the containing directory and all parents are marked as protected. Any reached file that is not *.foo and not protected is a directory to be deleted. Because of the -depth traversal order, a directory is always reached after the *.foo files that might protect it. Warning: minimally tested, remove the echo at your own risk.

find . -depth -name '*.foo' -o -type d | awk '{
    if ($0 ~ /\.foo$/) {
        while (sub("/+[^/]+$", "")) {protect[$0]=1;}
    } else {
        if (!protect[$0]) {
            gsub("[\\\001-/]", "\\\\&"); # protect file names for xargs
            print;
        }
    }
}' | xargs echo rm -rf

_{For once, I'm not proposing a zsh solution.}