I might approach the problem slightly differently, with an inverted character class:

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
[download]

Note that:

• A  ^ (caret) in the first position in a character class inverts the contents of the class.
• A  - (hyphen) in the first position in a character class (or in the first position after an initial caret, if there is one), or in the last position in the class is a literal hyphen character. Everywhere else it is a character range operator as in  A-Z and  0-9 elsewhere in the example class.
• The  $ @ characters should always be escaped, as otherwise they will often be interpreted as interpolable variables.
• Finally,  \x27 \x23 are how I have to represent the  ' # characters, respectively, because my REPL doesn't like these literal characters in  qr// and similar operators. (Have to fix that someday.)

(And a lot more test cases wouldn't be a bad idea.)

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