The command "rm -rf !(a)" doesn't work in bash -c syntax

There are three files in family dir named 'a' 'b' 'c'. I used "rm -rf !(a)" to delete the 'b' and 'c' files, after run it in bash CLI, it worked fine. As below:

xx@xx:~/# ls
a b c
xx@xx:~/# rm -rf !(a)
xx@xx:~/# ls
a

However, when I was running it by "bash -c", it threw a syntax error to me, that is as below:[![enter image description here]

xx@xx:~/# ls
a b c
xx@xx:~/# bash -c "rm -rf !(a)"
bash: -c: line 0: syntax error near unexpected token`('
bash: -c: line 0:`rm -rf !(a)'

Then I added backslash before '!', '(' and ')'. Although, there is not error occur; I found it did not work. As below:

xx@xx:~/# ls
a b c
xx@xx:~/# bash -c "rm -rf \!\(a\)"
xx@xx:~/# ls
a b c

Could any body can help to clarify this problem?

Don't use extglob patterns carelessly.
Don't use "not" logic carelessly.
Don't use globs carelessly.

And for all gods' sake, please don't use rm -fr as root with anything other than damned-near paranoia.

If you had anything besides a in that directory, or in any subdirectory of it, it's gone.

$: find
.
./a
./abc
./bar
./bcd
./efg
./efg/hij
./efg/hij/klm
./foo
./x
./y
./y/deleteme
./y/deleteme/stuff

$: bash -O extglob -c 'echo rm -fr !(x)'
rm -fr a abc bar bcd efg foo y

Obviously, it grabs everything that is, as you asked, not x.
As Ted Lyngmo pointed out in his comment above,
> rm -rf [^a] would do if you want to remove all one letter files and directories except a. If you want to remove b and c explicitly: rm -rf [bc] ... or rm -rf b c ...

Simple, clear, and specific is virtually always better when it's an option.

Added by Ted:

> If you want to remove all files except b and c in the current directory (which is what you asked for in a comment) you could again use find with the extension -maxdepth 1 to only make it search in the current directory:

find . -maxdepth 1 -type f \! \( -name b -o -name c \) -exec echo {} +

> Replace echo with rm -f if you are sure you want to delete those listed. The find version included in [tag:linux] has some more extensions making it possible to skip providing the top directory . and it also has a -delete option to delete files:

# danger zone below:
find -maxdepth 1 -type f \! \( -name b -o -name c \) -delete

(Thanks, Ted - I was just coming back to add this, lol)

> Paul Hodegs, you are right, however there is a case that i need keep some specified file or sub-dir in a certain dir, we need to remove the other dirty data in this dir regularly to avoid limited disk no-free case caused by some partners forgetting remove his/her research data in this dir after he or she used. –
Yayong Duan

Valid, in which case your original question is (sort of) a programming question. Be very careful to always assert that you are working in/on the right directory, and careful that maybe you back up your data pretty often against possible errors, but the important thing in that case is that you explicitly list ALL the files you want to keep in the single command to remove everything else.

In my above example, if you wanted to keep abc and bcd, you'd need rm -fr $thatDir/!(abd|bcd).

Just be super careful with that, and I strongly suggest using a nonprivileged user.