I have a string like 

```
<link rel='stylesheet' href='/abc/def/ghi/default.css' type='text/css' media='screen' />

```

Now, I want to just extract "/abc/def/ghi/default.css" and pass it to a function foo

```
void foo(string str)
{

//some logic
return str; //suppose it returns /abc/def/ghi/default.css/v=123
}

```

And i want to append it back to my original string like

```
<link rel='stylesheet' href='/abc/def/ghi/default.css/v=123' type='text/css' media='screen' />

```

i tried with substring, but alwals the content changes and i can start looking string from "href" but i dont know how long will the href be.