获取引号内的数字

I have a string that has a number inside exactly one pair of quotes. How can I get this number using php?

I have tried iterating over the string and or using str_split but I'm not sure how to limit it to what is inside the quotation marks. The fact that the number can be any length makes it even harder.

EDIT: Here is an example

Hello this is my "100"th string!,

I would need to return 100;

preg_match() is a way to get the number from string. Example:

$str = 'Hello this is my "100"th string!,';
preg_match('/\d+/', $str, $match);

echo $match[0];

Demo

echo intval('123string');

results in 123

trim the quotes from around the string, and php will immediately see the number inside.

$str = "'1234'";
$num = trim($str, "'\"");
echo $num + 1;
// => 1235

or if you have text as well a string, replace all non-digits with spaces, then have php automatically parse the string when it is used in an arithmetic expression.

$num = preg_replace('/\D/', ' ', $string) + 0;

use preg_replace:

echo preg_replace("~[^\d+]~", '', 'Hello this is my "100"th string!,');