Bug trying to preserve linebreak in curl request in bash

I have the following script that works perfectly:

payload='{"index":{}}'$'\n''{"name":"Samuel"}'
echo "$payload" > tmp.json
curl -X POST  "http://my.api.com/" \
  -H "Content-Type: application/json" \
  --data-binary @./tmp.json

I get a success response from my.api.com and I confirmed the entry made it into the database.

I don’t like that I am writing a tmp.json to disk. I prefer to send the payload variable as is directly to the curl statement. So I tried something like this:

payload='{"index":{}}'$'\n''{"name":"Samuel"}'
curl -X POST  "http://my.api.com/" \
  -H "Content-Type: application/json" \
  --data @- << echo "$payload"

But I get an error response from my.api.com saying there are line break issues and syntax issues. What Can I do to avoid writing the payload variable to disk?

I’ve tried many other things like:

--data "$payload"
--data `$payload`
--data @<(echo "$payload")
...etc...

But none of these are working.

>Solution :

<< is for here documents:

curl ... <<EOF
$payload
EOF

You want either a process substitution

curl ... < <(echo "$payload")

or a here string

curl ... <<< "$payload"

But if you already have the payload in a parameter, you don’t need @- anymore:

curl ... --data "$payload"

I’m not sure why that would be producing the error you claim.