Function is_valid_name 

pub fn is_valid_name(name: &str) -> bool

This function is used by UserBuilder and GroupBuilder to determine if a name for a user/group is valid. It is provided for convenience.

Usernames must match the POSIX standard for usernames . The “portable filename character set” is defined as A-Z, a-z, 0-9, and ._- (see here).

Usernames may not be more than 32 or less than 3 characters in length.