If you really want to restore a .bak into a MSSQL database, then do this

RESTORE DATABASE [database] FROM  DISK = N'/mnt/data/database.bak'
    WITH MOVE N'database' TO N'/var/opt/mssql/data/database.mdf',
    MOVE N'database_Log' TO N'/var/opt/mssql/log/database.ldf',
    RECOVERY,
    REPLACE;

Easy!

This is quite useful if you have a .bak file at your hand (maybe you have downloaded it from some internal file repository), or have some base data that you want to load into a fresh database (if you want to test out something on localhost). If you have a docker setup, then it is easy to map the .bak into your image, just use the -v parameter, when you call docker run: docker run -v /local/path:/docker/path alpine. Then you could have a local directory with your .bak files, fx called mssql, and then map it into your docker container, and then have script that connects to the docker container, and fires the above piece of sql!

Nice!!