UpdateTerraformVarFiles.ps1

Get-ChildItem -Path %teamcity.build.checkoutDir%\infra\ -Filter terraform.tfvars | 
Foreach-Object -Begin { Write-Host 'Processing tfvars files in directory'} {
    $file_name = $_.FullName
    Write-Host "Going to substitute variables in $file_name"
    $content = Get-Content $file_name
    for ($i = 0; $i -lt $content.Count; $i++) {
        $line = $content[$i].Split("#") #allow comments in a line
        if(![string]::IsNullOrEmpty($line[0])) { #do not process empty strings
            $var_definition = $line[0].Split("=")
            $var_name = $var_definition[0].Trim()
            $new_line ="$var_name = `"#{$var_name}`"" #format the updated line
            $content[$i] = $new_line
        }
    }
    $content | Set-Content -Path "$file_name" #write the result back to the same file
}