How do i get rid ofa part of a string?

If i had a string like this:

$a = "/home/name/public_html/dir/dir2/index.html";

how could i make $b = "/dir/dir2/index.html";

Any one know?

$BaseDir = "/home/name/public_html";
$a = "$BaseDir/dir/dir2/index.html";
$b = "$BaseDir/dir/dir3/index.html";


If thats not what you mean, then be more specific.

thanks, but thats not what i meant. But i found a better way to do what i wanted to do.