8.13. Extracting the Query from a URL
Problem
You want to extract the query from a string that holds a
URL. For example, you want to
extract param=value
from http://www.regexcookbook.com?param=value
or from /index.html?param=value
.
Solution
^[^?#]+\?([^#]+)
Regex options: Case insensitive |
Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby |
Discussion
Extracting the query 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 question mark. That is the first question mark
allowed anywhere in URLs. Thus, we can easily skip ahead to the first
question mark with ‹^[^?#]+\?
›. The question mark is a metacharacter
only outside character classes, but not inside, so we escape the literal
question mark outside the character class. The first ‹^
› is an
anchor (Recipe 2.5), whereas the second
‹^
› negates the character
class (Recipe 2.3).
Question marks can appear in URLs as part of the (optional)
fragment after the query. So we do need to use ‹^[^?#]+\?
›, rather than just ‹\?
›, to make sure we have the
first question mark in the URL, and make sure that it isn’t part of the
fragment in a URL without a query.
The query runs until the start of the fragment, or the end of the
URL if there is no fragment. The fragment is delimited from the rest of
the URL with a hash sign. Since hash signs are not permitted anywhere
except in the fragment, ‹[^#]+
› is all we need to match the query. The negated character class matches ...
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