cURL command data as input file substitute variables

I am trying to parametrise the confluent connector script - where I have externalised the variables that I am reading from a file and now I am trying to externalise the data part.

I am writing a wrapper shell script where I read the parameter file which has a format of var=value

How do I set-up my data file where I can use the variable substitution.

Is it possible to do it that way? How can I achieve it?

My current curl command is

curl --cert /clientcertslocation/certificate.pem --key /clientcertslocation/priv.key -k -X PUT -H "${HEADER}" --data @data.json "${CONNECT_SERVER_REST_API_PROTOCOL}://${CONNECT_SERVER}":8083/connectors/${CONNECTOR_NAME}/config

And the data.json looks like this

{
  "connector.class": "io.confluent.connect.s3.S3SinkConnector",
  "errors.log.enable": "true",
  "errors.log.include.messages": "false",
  "errors.tolerance": "all",
  "flush.size": "1",
  "locale": "en-US",
  "name": "${CONNECTOR_NAME}",
  "partition.duration.ms": "3600000",
  "partitioner.class": "io.confluent.connect.storage.partitioner.TimeBasedPartitioner",
  "path.format": "'event_creation_time='YYYY-MM-dd",
  "s3.region": "us-east-1",
  "s3.bucket.name": "${S3_BUCKET_NAME}",
  "s3.part.size": "76350000",
  "rotate.interval.ms":"90000",
  "schema.compatibility": "NONE",
  "schema.generator.class": "io.confluent.connect.storage.hive.schema.DefaultSchemaGenerator",
  "schema.registry.url": "${SR_URL}",
  "storage.class": "io.confluent.connect.s3.storage.S3Storage",
  "tasks.max": "${NO_OF_TASKS}",
  "timestamp.extractor": "RecordField",
  "timestamp.field": "EventCreatedTime",
  "timezone": "UTC",
  "topics": "${topics_list}",
  "topics.dir": "${SOURCE_SYSTEM_NAME}",
  "format.class": "io.confluent.connect.s3.format.avro.AvroFormat",
  "key.converter": "org.apache.kafka.connect.storage.StringConverter",
  "value.converter": "io.confluent.connect.avro.AvroConverter",
  "value.converter.schema.registry.url": "${SR_URL}"
}

Thank you

Running the data through a here-document will expand variables whilst preserving quotes:

#!/bin/sh

. parameter-file

eval "cat <<EOF
$(cat data.json)
EOF" |

curl \
--cert /clientcertslocation/certificate.pem \
--key /clientcertslocation/priv.key \
-k \
-X PUT \
-H "${HEADER}" \
--data @- \
"${CONNECT_SERVER_REST_API_PROTOCOL}://${CONNECT_SERVER}":8083/connectors/${CONNECTOR_NAME}/config

--data @- tells curl to read the data from stdin.

To avoid the possible security problems of eval, remove the need for indirection by hardcoding the data directly in the wrapper script:

curl ... --data @- <<EOF
{
    "connector.class": "io.confluent.connect.s3.S3SinkConnector",
...
    "value.converter.schema.registry.url": "${SR_URL}"
}
EOF