For example, you export apple.db to backup.sql with .dump or .schema as shown below. *backup.sql is created if it doesn't exist and .dump can export schema with data and .schema can export only schema and my answer explains how to export a database:
sqlite3 apple.db .dump > backup.sql
Or:
sqlite3 apple.db .schema > backup.sql
Now, you can import backup.sql into orange.db as shown below. *orange.db is created if it doesn't exist:
sqlite3 orange.db < backup.sql
Or:
sqlite3 orange.db
...
sqlite> .read backup.sql
Be careful, if you directly import apple.db into orange.db as shown below:
sqlite3 orange.db < apple.db
Or:
sqlite3 orange.db
...
sqlite> .read apple.db
Then, you get the error below:
Parse error near line 1: near "SQLite": syntax error