Looping over directories in Bash

Question

I have a fundamental question about how bash works, and a related practical question.

Fundamental question: suppose I am in a directory that has three subdirectories

Answer 1

This should work:

shopt -s nullglob   # empty directory will return empty list
for dir in ./*/;do
    echo "$dir"         # dir is directory only because of the / after *
done

To be recursive in subdirectories too, use globstar:

shopt -s globstar nullglob
for dir in ./**/;do
    echo "$dir" # dir is directory only because of the / after **
done

You can make @Adrian Frühwirths' method to be recursive to sub-directories by using globstar too:

shopt -s globstar
for dir in ./**;do
    [[ ! -d $dir ]] && continue # if not directory then skip
    echo "$dir"
done

From Bash Manual:

globstar

If set, the pattern ‘**’ used in a filename expansion context will match all files and zero or more directories and subdirectories. If the pattern is followed by a ‘/’, only directories and subdirectories match.

nullglob

If set, Bash allows filename patterns which match no files to expand to a null string, rather than themselves.