Regex backreference combined with string - how to separate

Question

Hi, 
I'm doing a replace with a backreference but the backreference is being interpreted as part of the string instead. If I insert a space it is interpreted correctly but I do not want to have a space.
Here's the code:
$regex = '(<add key="Global.LoadBalancer.ServerFarmIPAddresses.CSV"\svalue=")(?:[^"]+)("\s/>)'
$fillerString = '$1127.0.0.1$2'
The expected result should be to change this string:
<add key="Global.LoadBalancer.ServerFarmIPAddresses.CSV" value="10.10.10.10,10.10.10.9,10.128.128.211,10.128.128.111" /> 
And change it to this one:
<add key="Global.LoadBalancer.ServerFarmIPAddresses.CSV" value="127.0.0.1" /> 
But instead it changes it to this:
    $1127.0.0.1" />    
How can I separate the $1 from the Ip address without adding a space?

Answer 1

Put curly braces around the "1" and "2" in the replacement string:
$fillerString = '${1}127.0.0.1${2}'