how to get lambda symbol in header angular code example

Example: how to parse header in node.js lambda

{
    "method": "$context.httpMethod",
    "body" : $input.json('$'),
    "headers": {
        #foreach($param in $input.params().header.keySet())
        "$param": "$util.escapeJavaScript($input.params().header.get($param))"
        #if($foreach.hasNext),#end
        #end
    }
}