You can use Monetate's Full-Page Test experiences to redirect from URL A to URL B and add a new parameter value while keeping existing parameter value(s) intact.
For this use case,
site.com/?test=true should redirect to
site.com should redirect to
Within the regular expression (regex) are capture groups that correspond to the Replacement Page field below.
$1is the first capture group.
$2is the second capture group.
$3is the third capture group.
In this example, the regex preserves any parameter value(s) it identifies as the third capture group and then inserts it after the new parameter value to be added by using
$3 in the Replacement Page input.
Dissecting the Regular Expression
This URL regex consists of three capture groups and one negative lookahead group.
A negative lookahead only succeeds if the regex inside the lookahead fails to match.
First Capture Group
The initial piece of the first capture group,
https?:\/\/, matches for the unsecure (
http) and secure (
https) versions of the URL protocol for
site.com. By including an optional character with
s?, it can match for either
The second piece,
(?:www|m|t)\., matches for the subdomain. The vertical pipe (
|) character makes this into an array of OR options that matches for
t for desktop, mobile, or tablet top-level domains.
This example matches all top-level domain variants of the site
m.site (mobile) or
t.site (tablet), or
www.site (desktop). The question mark and colon (
?:) set this group to be a noncapture group.
The final piece of the first capture group,
site\.com\/, matches for the domain
site.com using the backslash escape character (
\) to precede any symbols needed as literal characters, such as the forward slash (
/) or the period (
Second Capture Group
The second capture group,
$|\?, checks if the URL either ends by using a dollar sign (
$) or looks for a parameter of any kind that's initialized with
Third Capture Group
The third capture group checks if any number of any characters exist after the parameter(s) with
Negative Lookahead Group
The negative lookahead group,
?!.*string=test, looks for what does not match
?! any number of any characters
.* followed by a literal string of characters that matches the parameter and value being appended during this Full-Page Test experience
This piece of the regex is extremely important and ensures a loop occurs of constant redirecting and appending another copy of the same parameter and value.
Once the regex is complete, you can see how it works in the Full-Page Test experience. The first part of the URL remains intact and is placed at the beginning of the redirect URL with
$1, then the parameter string and value
?string=test& is appended. Including the ampersand (
&) is very important because it preserves and appends any additional parameters and values captured in the third capture group that is added next with