Find and replace string in parameter bash

Question

$ ./myscript my.site.com

How do I replace all dots in the first parameter? Here's my current try but it's returning a bad substition error.

#!/bin/bash
dbname=${$1//./_}

echo $dbname

Answer 1

dbname=${1//./_}

因为$1和${1}是相同的，所以在1之前删除$ 。