Variables referenced inside single-quoted strings don't expand as you're expecting them to:

my $foo = 'Password';

printit('Foo is $foo');
printit("Foo is $foo");
printit($foo);

sub printit {
   my $val = shift;
   print "val=<$val>\n";
}
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If you run the above code, it'll give you:

val=<Foo is $foo>
val=<Foo is Password>
val=<Password>
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As you can see, the single-quoted string isn't giving you what you want. If you want the value to expand, use double-quoted strings.

So the first problem is that you're using single-quoted strings in places where a double-quoted string is more appropriate. (The first argument to the DBI->connect function). You're also using quoted strings where you don't even need them (the second and third arguments, for example).