Let us suppose you have 3 (or however many) databases that you want to work with in sqlite e.g. say you have a Dev, Test and a Production database which you want to transfer data between them.
Open a sqlite command prompt
Open to to the databases you want to work with using the .open command as well as the attach command
sqlite> .open /path/to/Dev.db
sqlite> attach '/path/to/Test.db' as test
sqlite> attach '/path/to/Productiom.db' as prod
Verify the opened databases using .databases command to confirm that you have all 3 databases opened
Now you can run sql statements against tables in any of the databases e.g.
For tables in Dev.db you can do a direct select * from tbl2 or insert into tbl2 etc
For table in the Test.db you will need to prefix the table name with the alias specifiedwhen you attached the Test.db i.e. test and likewise for Production.db tables you will need to prefix the tables with prod e.g. insert into test.tbl2 select * from prod.tbl2 to copydata from Production.db table into a Test.db table