shell post json格式问题

#!/bin/bash
post_url='https://test.com/post_json'
post_ip='sdsdsd'
post_mac='sdsddcxvxcvcvcv'
post_user='root'
PASSWORD='dssdsdsd'
#用单引号
curl -i -X POST -H "'Content-type':'application/json'" -d '{"post_ip":"'$post_ip'","post_mac":"'$post_mac'","post_user":"'$post_user'","PASSWORD":"'$PASSWORD'"}' $post_url