Replacing number in URL after matching substring pattern

Question

I need to insert a string right after a certain substring pattern in a URL and replace whatever number was there previously.

/ei/sort.do?layoutCollection=0&layoutCollectionProperty=&layoutCollectionState=0&pagerPage=1

I need to detect layoutCollectionState= and replace any number, here "0", by whatever number I need. I read about String's index and insert methods, but they dont exactly do the job I need them to do.

so if you have layoutCollectionState=2324 you want to replace 2324 by something else correct? — Cyzanfar
– Cyzanfar, Commented Oct 12, 2015 at 20:37

Jordan Running · Accepted Answer · 2015-10-12 21:24:10Z

3

URLs are complex and you'll save yourself a lot of work, and potential trouble, by using a library designed for manipulating them instead of trying to roll your own with regular expressions. Fortunately, Ruby comes with a few, among them URI. Using it is easy:

require "uri"

str = "/ei/sort.do?layoutCollection=0&layoutCollectionProperty=&layoutCollectionState=0&pagerPage=1"

# Create a URI object to easily get the query portion of the string
uri = URI(str)

# Decode the query values into a Hash
query = URI.decode_www_form(uri.query).to_h
# Or, if you're using Ruby 2.0 or earlier:
# query = Hash[URI.decode_www_form(uri.query)]

puts query
# => { "layoutCollection" => "0",
#      "layoutCollectionProperty" => "",
#      "layoutCollectionState" => "0",
#      "pagerPage" => "1"
#   }

# Change any values we want to change
query["layoutCollectionState"] = "SOME_OTHER_VALUE"

# Re-encode the query values and assign them back to the URI object
uri.query = URI.encode_www_form(query)

# Turn it back into a string
puts uri.to_s
# => /ei/sort.do?layoutCollection=0&layoutCollectionProperty=&
#    ... layoutCollectionState=SOME_OTHER_VALUE&pagerPage=1

And for what it's worth it needn't be that verbose:

def merge_query_values(url, hsh)
  URI(url).tap do |uri|
    uri.query = URI.encode_www_form(
                  URI.decode_www_form(uri.query).to_h.merge!(hsh) )
  end.to_s
end

str = "/ei/sort.do?layoutCollection=0&layoutCollectionProperty=&layoutCollectionState=0&pagerPage=1"

puts merge_query_values(str, "layoutCollectionState" => "SOME_OTHER_VALUE",
                             "foo" => "BAR")
# => /ei/sort.do?layoutCollection=0&layoutCollectionProperty=&
#    ... layoutCollectionState=SOME_OTHER_VALUE&pagerPage=1&foo=BAR

edited Oct 12, 2015 at 21:24

answered Oct 12, 2015 at 20:40

Jordan Running

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5 Comments

engineersmnky Over a year ago

This is the most proper way to manipulate a url but definitely will require some additional handling for things like layoutCollectionState not being present or a malformed URI but I would definitely recommend this especially if they needed additional manipulation.

the Tin Man Over a year ago

You had a badly formatted trailing code snippet for merge_query_values. I corrected the formatting but you'll need to edit to decide which definition of merge_query_values you want to display, or explain why the second definition is significant.

Jordan Running Over a year ago

Oops. Thanks @theTinMan. I meant to delete the second; it was overly clever and didn't work quite right. ;)

the Tin Man Over a year ago

"Ruby comes with a few"... well, no. It comes with URI. Addressable::URI is an available gem that is more full-featured.

Jordan Running Over a year ago

It also comes with CGI. So that's two. And if you're using Rails you've already got Rack::Utils loaded.

the Tin Man · Accepted Answer · 2015-10-12 21:29:35Z

2

The simple way would be to use String#gsub with a regex pattern like so

s = '/ei/sort.do?layoutCollection=0&layoutCollectionProperty=&layoutCollectionState=0&pagerPage=1'
s.gsub(/(?<=layoutCollectionState=)\d+/,'4') 
#=>"/ei/sort.do?layoutCollection=0&layoutCollectionProperty=&layoutCollectionState=4&pagerPage=1"

Here I substituted "0" for "4" (change "4" to whatever you want to use).

This uses a look behind pattern ((?<=layoutCollectionState=)) and then captures the digits that follow this pattern as the item to be replaced. It then replaces this with the second parameter ("4" in this case)

edited Oct 12, 2015 at 21:29

the Tin Man

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answered Oct 12, 2015 at 20:31

engineersmnky

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2 Comments

the Tin Man Over a year ago

While it's pretty safe changing a numeric value, using sub or gsub with alpha substitution isn't a good idea as it'd be easy to inject invalid characters resulting in an incorrectly encoded URL. That's why we use tools like URI or Addressable::URI, which are aware of the specs.

engineersmnky Over a year ago

@theTinMan I am aware of the implications and endorsed Jordans answer. Thank you for your comment but I think you meant that's why we 'have' tools like URI. This solution adequately answers the question and maintains spec when used as directed. The tools used are the choice of the creator not the viewer.

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