c:\@Work\Perl\monks>perl -wMstrict -le
"use constant NOT_ALLOWED => qr{ [^-\x27\x23\$\@0-9a-zA-Z.\\/_%(){}&!~`^] }xms;
 ;;
 for my $str ('',  qw(ABC_ABC  'A'  ///?///  =*+|  ABC=),  ' ',  qq{\t\r\n}) {
   my $status = 0 + $str =~ NOT_ALLOWED;
   print qq{[$str] $status};
   }
"
[] 0
[ABC_ABC] 0
['A'] 0
[///?///] 1
[=*+|] 1
[ABC=] 1
[ ] 1
[
] 1