Question

I would like to take out a parameter from a URL by its name without knowing which parameter it is, and reassemble the URL again.

I guess it is not that hard to write something on my own using CGI or URI, but I imagine such functionality exists already. Any suggestions?

In:

http://example.com/path?param1=one&param2=2&param3=something3

Out:

http://example.com/path?param2=2&param3=something3

Answer 1

The addressable gem will do this nicely; please see the superior answer by The Tin Man. But if you want to roll your own, here’s how. The only claim this code has to elegance is that it hides the ugly in a method:

#!/usr/bin/ruby1.8

def reject_param(url, param_to_reject)
  # Regex from RFC3986
  url_regex = %r"^(([^:/?#]+):)?(//([^/?#]*))?([^?#]*)(\?([^#]*))?(#(.*))?$"
  raise "Not a url: #{url}" unless url =~ url_regex
  scheme_plus_punctuation = $1
  authority_with_punctuation = $3
  path = $5
  query = $7
  fragment = $9
  query = query.split('&').reject do |param|
    param_name = param.split(/[=;]/).first
    param_name == param_to_reject
  end.join('&')
  [scheme_plus_punctuation, authority_with_punctuation, path, '?', query, fragment].join
end   

url = "http://example.com/path?param1=one&param2=2&param3=something3"
p url
p reject_param(url, 'param2')

# => "http://example.com/path?param1=one&param2=2&param3=something3"
# => "http://example.com/path?param1=one&param3=something3"