Update: I misread the question. You can still find some advice here, but my reply doesn't fully answer your question.

Your regex checks that the password has at least one word character somewhere, followed by at least one digit, followed by an at-sign, or it contains an octothorpe, or it contains a dollar sign, or a percent sign, or a backslash, or a forward slash.

Use a character class intead. You need to escape ], $, \, and - in it, nothing else. You need to escape a slash, too, because it's the delimiter of the whole regex.

You can use a regex match to check both the valid characters and the length of the password:

#!/usr/bin/perl
use warnings;
use strict;
use feature qw{ say };

print 'Enter the password: ';
chomp( my $password = <> );
if ($password =~ /^[\w\d@#\$%`~!^&*()_\-+={}[\]|\\'";:\/?.><,]{8}$/) {
    say "You're now authenticated.";
} else{
    say 'Please enter the correct password';
}
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