Instead of creating indexes, we could use the indexed array
already available in BerkeleyDB
using the recno structure;
then, we walk along the cursor from any desired line_num.
The database, of course, is always update-table.
This command constructs such Recno database
from our given text file: cat foo.txt | db4.3_load -T -t recno bar.db
Although simple, the command above needs further refinement if we are
unsatisfied with the default definition of newline, with the escaping of
inserted text, or problems due to binary input. (See db4.3_load(1) )