How do I store last 4 characters of a string in a variable?

[jewel464g]

I need to get the last four characters of a string and store them in a variable called tax.

the string contains "Dublin0.07"
I want to store the last four characters in a variable named $tax so that $tax = 0.07 I am assuming that the decimal is considered a character.

I found this and it works but I'm sure there is a better way.
$str = "Dubline0.07";
$four = $str{strlen($str)-1};
$three = $str{strlen($str)-2};
$two = $str{strlen($str)-3};
$one = $str{strlen($str)-4};

$tax = "$one" . "$two" . "$three" . "$four";

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[ericbrunson]

Use substr with a negative start

$rest = substr("abcdef", -4);    // sets $rest to "cdef"
$rest = substr("abcdef", -4, 2); // sets $rest to "cd"