json -- shell script execution in json -

i have working json scrip in using shell script, trying pass arguments shell script, tryed few options getting syntax error. please advice how pass arguments following json.

"fn::base64": {         "fn::join": ["", ["#!/bin/bash\n",                 "cd /tmp\n",                 "curl -ko https://example_git_url/script.sh\n",                 "chmod 755 userdata.sh\n",                 "/tmp/script.sh\n"         ]]