Finds all tokens in a string when surrounded by curly brackets. Values are substituted from environment variables. Perfect for CI/CD pipelines.

Find-ReplaceToken.ps1

<#

.SYNOPSIS
Replace tokens in a file with values from environment variables. 

.DESCRIPTION
Finds tokens in a given file and replace them with values from environment variables. It is best used to replace configuration values in a release pipeline.
Tokens are found when enclosed with curly brackets. For eample: {{ foo }}

.EXAMPLE

$env:URL="http://localhost:8080"
$env:USERNAME="admin"
$env:PASSWORD="Test123"

config.template.json:
{
  "url": "{{URL}}",
  "username": "{{ USERNAME }}",
  "password": "{{PASSWORD}}"
}

. ./Find-ReplaceToken.ps1
Find-ReplaceToken -String (Get-Content config.template.json -Raw) | Out-File config.json

config.json (result):
{
  "url": "http://localhost:8080",
  "username": "admin",
  "password": "Test123"
}

.NOTES
Inspired by this other Gist: https://gist.github.com/niclaslindstedt/8425dbc5db81b779f3f46659f7232f91
#>
function Get-EnvironmentVariable {
    param (
        $Variable
    )
    
    (Get-Item -Path Env:$Variable).Value
}

function Find-ReplaceToken {
    [CmdletBinding()]
	param(
		[string]$String
	)

	$Result = $String | Select-String -Pattern "\{\{ ?(\w*?) ?\}\}" -AllMatches

    $EnvironmentVariablesMap = @{}

    foreach($Match in $Result.Matches){
        if ($Match.Groups)
        {
            for($i = 1; $i -lt $Match.Groups.Count; $i++){
                $VariableName = $Match.Groups[$i].Value

                $VariableValue = Get-EnvironmentVariable -Variable $VariableName

                $EnvironmentVariablesMap[$VariableName] = $VariableValue
            }          

        }
    }

    foreach($Entry in $EnvironmentVariablesMap.GetEnumerator()){
        $String = $String -replace "\{\{ ?($($Entry.Key)*?) ?\}\}",$Entry.Value
    }

    $String
}