Resource Manager (ARM) Template with copyIndex variable to output

template.json

{
  "$schema": "https://schema.management.azure.com/schemas/2015-01-01/deploymentTemplate.json#",
  "contentVersion": "1.0.0.0",
  "parameters": {
    "storageSettings": {
      "type": "object",
      "defaultValue": {
        "count": 3,
        "prefix": "baa"
      }
    }
  },
  "variables": {
    "storageSettings": "[parameters('storageSettings')]",
    "storage": {
      "copy": [
        {
          "name": "accounts",
          "count": "[parameters('storageSettings').count]",
          "input": {
            "name": "[concat(parameters('storageSettings').prefix, uniqueString(resourceGroup().id, string(copyIndex('accounts'))))]",
            "resourceGroup": "[resourceGroup().name]"
          }
        }
      ]
    }
  },
  "resources": [
    {
      "name": "[variables('storage').accounts[copyIndex()].name]",
      "type": "Microsoft.Storage/storageAccounts",
      "apiVersion": "2016-12-01",
      "sku": {
        "name": "Standard_LRS"
      },
      "kind": "Storage",
      "location": "[resourceGroup().location]",
      "tags": {},
      "properties": {
      },
      "copy": {
        "name": "storageCopy",
        "count": "[variables('storageSettings').count]"
      }
    }
  ],
  "outputs": {
    "storageAccounts": {
      "value": "[variables('storage').accounts]",
      "type": "array"
    }
  }
}

Thank You :-)