>perl -wMstrict -le
"my $min_10   = qr{ (?= .{10})          }xms;
 my $a_digit  = qr{ (?= .* \d)          }xms;
 my $a_lower  = qr{ (?= .* [[:lower:]]) }xms;
 my $an_upper = qr{ (?= .* [[:upper:]]) }xms;
 my $special  = qr{ [@\#\$%^&+=]        }xms;
 my $a_spec   = qr{ (?= .* $special)    }xms;
 my $valid = qr{
   \A $min_10 (?: $a_digit $a_lower $an_upper $a_spec){3,}
   }xms;
 while (chomp(my $pw = <STDIN>)) {
   my $ok = $pw =~ $valid;
   print qq{'$pw' }, $ok ? 'valid' : 'INVALID';
   }
"
(?: (?msx-i: (?= .* \d)          ) (?msx-i: (?= .* [[:lower:]]) ) (?msx-i: (?= .
* [[:upper:]]) ) (?msx-i: (?= .* (?msx-i: [@\#\$%^&+=]        ))    )){3,}
                    matches null string many times in regex; marked by <-- HERE
in m/                                                                   \A (?msx
-i: (?= .{10})          ) (?: (?msx-i: (?= .* \d)          ) (?msx-i: (?= .* [[:
lower:]]) ) (?msx-i: (?= .* [[:upper:]]) ) (?msx-i: (?= .* (?msx-i: [@\#\$%^&+=]
        ))    )){3,}                          <-- HERE / at -e line 1.

'' INVALID

' ' INVALID
x
'x' INVALID
xxxxxxxxx
'xxxxxxxxx' INVALID
xxxxxxxxxx
'xxxxxxxxxx' INVALID
%Aa123456
'%Aa123456' INVALID
%Aa1234567
'%Aa1234567' valid
1aA%23456
'1aA%23456' INVALID
1aA%234567
'1aA%234567' valid
Terminating on signal SIGINT(2)