How do I convert a binary string to a number in Perl?

My preferred way is:

$x_num = oct("0b" . $x_bin);

Quoting from man perlfunc:

    oct EXPR
    oct     Interprets EXPR as an octal string and returns the
            corresponding value. (If EXPR happens to start
            off with "0x", interprets it as a hex string. If
            EXPR starts off with "0b", it is interpreted as a
            binary string. Leading whitespace is ignored in
            all three cases.)