Use docker cp to copy your files into the running container instance. From there, you should be able to docker exec sql bash to give you a prompt inside the container instance, or you can run the command directly.

docker cp YOURFILE sqlcontainername:/tmp/YOURFILE
docker exec sqlcontainername \
  /opt/mssql-tools/bin/sqlcmd  \
  -j -I -S localhost -U sa -P "YOURSAPASS" \
  -i /tmp/YOURFILE
docker exec sqlcontainername rm /tmp/YOURFILE

Your command may not be sqlcmd, but the above should point you or anyone seeing this in the right direction.

I automate using node/npm scripts with shelljs, there’s also a docker-cli-js package.

// copies and runs a local sql script file inside the 
// docker container's instance
const runSqlScript = (scriptPath, container) => {
  console.log(`Running SQL Script (${scriptPath})`);
  // copy the local file into the container
  shell.exec(`docker cp "${scriptPath}" ${container}:/tmp/temp.sql`);
  // execute the file in the container on sql
  shell.exec(
    `docker exec -i ${container}/opt/mssql-tools/bin/sqlcmd -S localhost -U sa -P "Let_Me_In" -i /tmp/temp.sql -j -I`
  );
  // remove the file inside the container
  shell.exec(`docker exec ${container}rm /tmp/temp.sql`);
};