Parameter value based on an Environment Variable, as an Array

[wk7804]

I would like to define an environment variable whose value would be treated as an array when processing my Bicep template.
I am using 'az deployment sub create' command that is executed by a Bash script that is defining and exporting environment variables .
I am also using a .bicepparam file where the parameter values are all being provided by readEnvironmentVariable().

In my specific case, I have 1 or more IP Address Prefixes where each need to be used in a separate outbound NSG Rule.
If I was defining the array directly in the .bicepparam file, it might look like this:

param prefixes = [
    '10.194.1.0/24'
    'fde4:3dff:59c2:1::/64'
 ]

I would then loop through these prefixes, using each in a separate rule:

param prefixes array

resource allowOutboundRules 'Microsoft.Network/networkSecurityGroups/securityRules@2023-09-01' = [for (prefix, i) in prefixes: {
  name: 'AllowOutbound${i}'
  parent: nsg
  properties: {
    [...]
    priority: allowOutboundStartingRuleNumber + i
    destinationAddressPrefix: prefix
  }
}]

What I am struggling with is how to provide a value that can be treated as an array when in the .biccepparm file I have this:

param prefixes: readEnvironmentVariable('PREFIXES')

I started with the approach below, and tried several variations, none of which result in an array containing each prefix as an individual entry:

PREFIXES="10.194.1.0/24, fde4:3dff:59c2:1::/64"

Put another way, the question could be: "How can I parse a multi-value string into an array with Bicep?".

Any suggestions would be appreciated!

[wk7804]

Apparently the solution was so obvious that I complete overlooked it :-{

Defining the environment variable like this:
PREFIXES="10.194.1.0/24,fde4:3dff:59c2:1::/64"

Then adding this:
var allowed = split(prefixes, ',')

Finally looping over the result did exactly what I needed.

[ChalksHome]

param dnsServers = array(split(readEnvironmentVariable('dnsServers', 'Values missing'),','))