Hassan and Brian, thanks for your answer.
This is the code I'm using:

tbls = db.execute("SELECT name FROM sqlite_master
                    WHERE type='table' ORDER BY name")
tbls.each do |tnam|
  ... some code
end

When using Ruby 1.8.7 I get the expected table names
as TAB1 TAB2 etc, but with 1.9.1 I get [["TAB1"]["TAB2"]] etc
and the 'some code' line does not execute because the table
name includes the square brackets and quotes.
I have done several test, even with sqlite-ruby and amalgalite
and I'm pretty sure something has changed in Ruby, as changing
only the Ruby version changes the value format returned.
I guess will need to use the to_i func as suggested, and wait
for better times...

Thanks for your time, Andreu.