将bash shell变量传递给jq过滤器

试图将bash shell变量传递到jq过滤器中

Trying to pass a bash shell variable into a jq filter

JSON:

{
"server1": {
"port": 3333,
"name": "foo",
"timesincelast": 248054
},
"server2": {
"port": 4444,
"name": "bar",
"timesincelast": 248054
  }
  }

尝试执行的Bash命令:

Bash command trying to execute:

 servername='server1'
 jq --arg servername "$servername" '.$servername .port'

但是遇到错误

 jq: error: syntax error, unexpected '$' (Unix shell quoting issues?) at 
<top-level>, line 1:

但是直接替换有效

jq '.server1 .port'