if ( $vlan_name =~ m|^\w[\w-]*$| ){
  # Name complies with :
  # * At least one char
  # * Starts with a letter, number or underscore
  # * Contains only alpha, num, underscore, hyphem
}else{
  # Complain about non-compliant name
}

##</code><code>##

 if ($vlan_number =~ m|^\d+$|) {
     # Compliant - numeric only
  }else{
    # Something Not completely numeric - display error.
  }