Directory Management – How to Rename Multiple Directories

This decrementing can be done in a pretty low-tech way: generate the list, start at the beginning. It's not that easy to “productize” by handling all cases, but it's little more than a one-liner if you're willing to hard-code things like the maximum number of digits and to assume that there are no other files called dir.*. Using bash syntax, tuned towards less typing:

i=0
for x in dir.{?,??,???}; do
  mv "$x" "${x%.*}.$i"
  ((++i))
done

Note that it has to be dir.{?,??,???} and not dir.* to get dir.9 before dir.10.

In zsh you could make this a little more robust at no cost, by using <-> to expand to any sequence of digits and (n) to sort numerically (dir.9 before dir.10).

i=0
for x in dir.<->(n); do
  mv $x ${x%.*}.$i
  ((++i))
done

I would go about this in a different way - specifically, using a depth-first search in place of the shell globstar **

For example, using GNU find, given:

$ tree
.
└── dir
    ├── foo
    │   └── baz
    │       └── MainFoo.c
    └── Foo
        ├── baz
        └── MainFoo.c

5 directories, 2 files

then

find . -depth -iname '*foo*' -execdir rename -- 's/Foo/Bar/;s/foo/bar/' {} +

results in

$ tree
.
└── dir
    ├── bar
    │   └── baz
    │       └── MainBar.c
    └── Bar
        ├── baz
        └── MainBar.c

5 directories, 2 files