If you're using PostgreSQL and need to retrieve the last inserted id then http://stackoverflow.com/a/2944481/89783 has all the details you need. The best seems to be using the RETURNING keyword to retrieve your identifier. Here's what it looks like for a table with an id field:
INSERT INTO persons (lastname,firstname) VALUES ('Smith', 'John') RETURNING id;
To dump the contents of a SQLite database out to a file containing SQL commands to CREATE tables and INSERT data use the following:
.output file.sql .dump
You can optionally specify a table name after .dump to just export that.
Find matching lines between 2 files
If you need to find what lines occur in two files then you'll find comm to be useful for that.
comm -12 file file2