How to loop over directories in Linux?

cd /tmp
find . -maxdepth 1 -mindepth 1 -type d -printf '%f\n'

A short explanation:

• find finds files (quite obviously)

• . is the current directory, which after the cd is /tmp (IMHO this is more flexible than having /tmp directly in the find command. You have only one place, the cd, to change, if you want more actions to take place in this folder)

• -maxdepth 1 and -mindepth 1 make sure that find only looks in the current directory and doesn't include . itself in the result

• -type d looks only for directories

• -printf '%f\n prints only the found folder's name (plus a newline) for each hit.

Et voilà!

All answers so far use find, so here's one with just the shell. No need for external tools in your case:

for dir in /tmp/*/     # list directories in the form "/tmp/dirname/"
do
    dir=${dir%*/}      # remove the trailing "/"
    echo "${dir##*/}"    # print everything after the final "/"
done