Linux print file and use it in for example a curl request

Question

This might be a complete noob question, but I would like to know a simple oneliner to solve my problem.

Imagine following: I have 5 files, could be .txt, .sql .anything.

root@DESKTOP:/$ ls
test.sql test1.sql test2.sql test3.sql

Imagine I would like to use for example test.sql in a curl request as part of a json parameter.

root@DESKTOP:/$ cat test.sql | 
curl -H "Accept: application/json" 
-H "Content-type: application/json" 
-X POST -d "{ \"sqlcommand\" :\"??????" }" 
http://localhost:9999/api/testsql

How can I put the output of the cat command in this request at the place of the questionmark? $0, $1 etc are not sufficient. I know how to do it with a for loop. And I could write a shell script that takes an input parameter that I could paste in the command. But. I would like to do it in a simple oneliner and moreover I'd like to learn how I can get the output of the previous command when I need to use it combined with other data OR when it is bad practice i'd like to know the best practice.

Thank you in advance!

Answer 1

This should do what you need:

curl -X POST -d "{ \"sqlcommand\" :\"$(cat test.sql)\" }" 

$(cmd) substitutes the result of cmd as a string