I needed to create a large directory structure for some testing. I hacked together this quick script that makes a small or large directory tree easily. You define how many branch points there are and how many branches each branch has all the way from the trunk to the leaves.

#!/bin/bash

i=0;
l=0;
levels=2
dirsperlevel=3

rm -rf tree
mkdir tree && cd tree

while [ $i -lt $levels ];
do
  for j in `find . -mindepth $i -maxdepth $i -type d`
  do
    pushd $j > /dev/null 2>&1
    for k in `seq 1 $dirsperlevel`;
    do
      mkdir $k;
    done;
    popd > /dev/null 2>&1
  done;
  i=$(($i+1))
  l=`echo "($dirsperlevel^$i)+$l"|bc`
done;

echo "$l dirs created in ./tree"

using 2 levels, and 3 directories per level we get 12 total directories created like so:

# mktree.sh 
12 dirs created in ./tree
# find tree    
tree
tree/2
tree/2/2
tree/2/3
tree/2/1
tree/3
tree/3/2
tree/3/3
tree/3/1
tree/1
tree/1/2
tree/1/3
tree/1/1

using something like 6 levels and 6 directories per level would give us 55,986 total directories.