Getting parts of a URL (Regex)

Question

Given the URL (single line):
http://test.example.com/dir/subdir/file.html

How can I extract the following parts using regular expressions:

1. The Subd

Answer 1

The regex to do full parsing is quite horrendous. I've included named backreferences for legibility, and broken each part into separate lines, but it still looks like this:

^(?:(?P\w+(?=:\/\/))(?::\/\/))?
(?:(?P(?:(?:&(?:amp|apos|gt|lt|nbsp|quot|bull|hellip|[lr][ds]quo|[mn]dash|permil|\#[1-9][0-9]{1,3}|[A-Za-z][0-9A-Za-z]+);)|[^\/?#:]+)(?::(?P[0-9]+))?)\/)?
(?:(?P(?:(?:&(?:amp|apos|gt|lt|nbsp|quot|bull|hellip|[lr][ds]quo|[mn]dash|permil|\#[1-9][0-9]{1,3}|[A-Za-z][0-9A-Za-z]+);)|[^?#])+)\/)?
(?P(?:(?:&(?:amp|apos|gt|lt|nbsp|quot|bull|hellip|[lr][ds]quo|[mn]dash|permil|\#[1-9][0-9]{1,3}|[A-Za-z][0-9A-Za-z]+);)|[^?#])+)
(?:\?(?P(?:(?:&(?:amp|apos|gt|lt|nbsp|quot|bull|hellip|[lr][ds]quo|[mn]dash|permil|\#[1-9][0-9]{1,3}|[A-Za-z][0-9A-Za-z]+);)|[^#])+))?
(?:#(?P.*))?$

The thing that requires it to be so verbose is that except for the protocol or the port, any of the parts can contain HTML entities, which makes delineation of the fragment quite tricky. So in the last few cases - the host, path, file, querystring, and fragment, we allow either any html entity or any character that isn't a ? or #. The regex for an html entity looks like this:

$htmlentity = "&(?:amp|apos|gt|lt|nbsp|quot|bull|hellip|[lr][ds]quo|[mn]dash|permil|\#[1-9][0-9]{1,3}|[A-Za-z][0-9A-Za-z]+);"

When that is extracted (I used a mustache syntax to represent it), it becomes a bit more legible:

^(?:(?P(?:ht|f)tps?|\w+(?=:\/\/))(?::\/\/))?
(?:(?P(?:{{htmlentity}}|[^\/?#:])+(?::(?P[0-9]+))?)\/)?
(?:(?P(?:{{htmlentity}}|[^?#])+)\/)?
(?P(?:{{htmlentity}}|[^?#])+)
(?:\?(?P(?:{{htmlentity}};|[^#])+))?
(?:#(?P.*))?$

In JavaScript, of course, you can't use named backreferences, so the regex becomes

^(?:(\w+(?=:\/\/))(?::\/\/))?(?:((?:(?:&(?:amp|apos|gt|lt|nbsp|quot|bull|hellip|[lr][ds]quo|[mn]dash|permil|\#[1-9][0-9]{1,3}|[A-Za-z][0-9A-Za-z]+);)|[^\/?#:]+)(?::([0-9]+))?)\/)?(?:((?:(?:&(?:amp|apos|gt|lt|nbsp|quot|bull|hellip|[lr][ds]quo|[mn]dash|permil|\#[1-9][0-9]{1,3}|[A-Za-z][0-9A-Za-z]+);)|[^?#])+)\/)?((?:(?:&(?:amp|apos|gt|lt|nbsp|quot|bull|hellip|[lr][ds]quo|[mn]dash|permil|\#[1-9][0-9]{1,3}|[A-Za-z][0-9A-Za-z]+);)|[^?#])+)(?:\?((?:(?:&(?:amp|apos|gt|lt|nbsp|quot|bull|hellip|[lr][ds]quo|[mn]dash|permil|\#[1-9][0-9]{1,3}|[A-Za-z][0-9A-Za-z]+);)|[^#])+))?(?:#(.*))?$

and in each match, the protocol is \1, the host is \2, the port is \3, the path \4, the file \5, the querystring \6, and the fragment \7.