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Regular Expressions Cookbook by Steven Levithan, Jan Goyvaerts

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7.14. Extracting the Fragment from a URL

Problem

You want to extract the fragment from a string that holds a URL. For example, you want to extract top from http://www.regexcookbook.com#top or from /index.html#top.

Solution

#(.+)
Regex options: Case insensitive
Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby

Discussion

Extracting the fragment from a URL is trivial if you know that your subject text is a valid URL. The query is delimited from the part of the URL before it with a hash sign. The fragment is the only part of URLs in which hash signs are allowed, and the fragment is always the last part of the URL. Thus, we can easily extract the fragment by finding the first hash sign and grabbing everything until the end of the string. #.+ does that nicely. Make sure to turn off free-spacing mode; otherwise, you need to escape the literal hash sign with a backslash.

This regular expression will find a match only for URLs that actually contain a fragment. The match consists of just the fragment, but includes the hash sign that delimits the fragment from the rest of the URL. The solution has an extra capturing group to retrieve just the fragment, without the delimiting #.

If you don’t already know that your subject text is a valid URL, you can use one of the regexes from Recipe 7.7. The first regex in that recipe captures the fragment, if one is present in the URL, into capturing group number 13.

See Also

Recipes 2.9, 3.9, and 7.7

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