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5. Query string

Available inall subroutines.

Returns the given URL but only keeps the parameters matching a regular expression. Groups within the regular expression are treated as if they were written as non-capturing groups. For example:

if (req.url.qs ~ "key-(?:[0-9]|\w)=([^&]*)-([^&]*)") { # captures to re.group.1 and re.group.2
  set req.url = querystring.regfilter_except(req.url, "key-([0-9]|\w)"); # does not capture
  set req.http.X-Key-1 = re.group.1;
  set req.http.X-Key-2 = re.group.2;
}

The "key-([0-9]|\w)" pattern shown here behaves as if it were written as a non-capturing group, "key-(?:[0-9]|\w)", ensuring the contents of re.group.1 and re.group.2 are not affected by the call to querystring.regfilter_except.

In this example, with a url of /example?key-1=image-abc&something-else=xyz the captured groups re.group.1 and re.group.2 would be image and abc respectively.

We're using ([^&]*) rather than (.*) for the group capture from req.url.qs. This is because we don't actually want to match every character, which would include the &something-else... part. We only want to match up to the start of the following key in the query string.