REPACE CHARS

[Andre]

Hi
How can y give s sbstition order of the kind
@string=~s/nonalfanum//g;
in these two cases?
1-wich will search and replace with "" (empty char) all nunnumeric or nonalphabetic 
chars?
2-wich will search and replace with "" (empty char) all nunnumeric or nonalphabetic 
chars with the exception of "-","_","@","." ?
Thanks