I have a problem with a regular expression to not allow special characters in file names.

I used the following expression ^[_0-9a-zA-Z\.]+$ which allows alphabetical characters, numbers, '_' and '.'.  I don't allow '-' in files names.
 
The result is that It doens't allow the creation  of a file named xx&yy or xx-yy.
It also doesn't allow to rename a file xx&yy but renaming a file xx-yy works.

And I don't understand why :-( the character '-' is accepted when it is a rename operation.

Thanks for your help.

Samira