How do I dump the data of some SQLite3 tables?

You're not saying what you wish to do with the dumped file.

To get a CSV file (which can be imported into almost everything)

.mode csv 
-- use '.separator SOME_STRING' for something other than a comma.
.headers on 
.out file.csv 
select * from MyTable;

To get an SQL file (which can be reinserted into a different SQLite database)

.mode insert <target_table_name>
.out file.sql 
select * from MyTable;

You can specify one or more table arguments to the .dump special command, e.g.sqlite3 db ".dump 'table1' 'table2'".

Not the best way, but at lease does not need external tools (except grep, which is standard on *nix boxes anyway)

sqlite3 database.db3 .dump | grep '^INSERT INTO "tablename"'

but you do need to do this command for each table you are looking for though.

Note that this does not include schema.

Any answer which suggests using grep to exclude the CREATE lines or just grab the INSERT lines from the sqlite3 $DB .dump output will fail badly. The CREATE TABLE commands list one column per line (so excluding CREATE won't get all of it), and values on the INSERT lines can have embedded newlines (so you can't grab just the INSERT lines).

for t in $(sqlite3 $DB .tables); do
    echo -e ".mode insert $t\nselect * from $t;"
done | sqlite3 $DB > backup.sql

Tested on sqlite3 version 3.6.20.

If you want to exclude certain tables you can filter them with $(sqlite $DB .tables | grep -v -e one -e two -e three), or if you want to get a specific subset replace that with one two three.

The best method would be to take the code the sqlite3 db dump would do, excluding schema parts.

Example pseudo code:

SELECT 'INSERT INTO ' || tableName || ' VALUES( ' || 
  {for each value} ' quote(' || value || ')'     (+ commas until final)
|| ')' FROM 'tableName' ORDER BY rowid DESC

See: src/shell.c:838 (for sqlite-3.5.9) for actual code

You might even just take that shell and comment out the schema parts and use that.

You could do a select on the tables inserting commas after each field to produce a csv, or use a GUI tool to return all the data and save it to a csv.