How to add content from a file to a table automatically

[Darlan Cavalcante Moreira <darcamo@gmail.com>]

Is there a way to detect when a file changes and then add the content from
it (if any, the file could be empty) to a specified org-mode table? Each
line in that file is already constructed in a way that it could be copied
and pasted to the table directly (but I can change that if it makes things
easier).

For instance, suppose I have the table below

--8<---------------cut here---------------start------------->8---
#+TBLNAME: FoodJanuary2013
|   | *Place*   | *Date*           | *Debit (R$)* | *Credit (R$)* |
|---+-----------+------------------+--------------+---------------|
|   | Some name | [2013-01-07 Seg] |         0.00 |         10.00 |
|---+-----------+------------------+--------------+---------------|
| # |           | *Total*          |         0.00 |         10.00 |
#+TBLFM: @3$4=vsum(@2..@-1);%.2f::@3$5=vsum(@2..@-1);%.2f
--8<---------------cut here---------------end--------------->8---

and a file "food.txt" that was modified externally (Dropbox sync) and now
has the content below

--8<---------------cut here---------------start------------->8---
| # | place name | [2013-01-08 Ter] | 0.00 | 12.50 |
| # | other place | [2013-01-09 Qua] | 9.30 | 0.00 |
--8<---------------cut here---------------end--------------->8---

I'd like the table to be automatically updated to include these two new
lines so that it should now corresponds to

--8<---------------cut here---------------start------------->8---
#+TBLNAME: FoodJanuary2013
|   | *Place*     | *Date*           | *Debit (R$)* | *Credit (R$)* |
|---+-------------+------------------+--------------+---------------|
|   | Some name   | [2013-01-09 Qua] |         0.00 |         10.00 |
| # | place name  | [2013-01-08 Ter] |         0.00 |         12.50 |
| # | other place | [2013-01-09 Qua] |         9.30 |          0.00 |
|---+-------------+------------------+--------------+---------------|
| # |             | *Total*          |         9.30 |         22.50 |
#+TBLFM: @5$4=vsum(@2..@-1);%.2f::@5$5=vsum(@2..@-1);%.2f
--8<---------------cut here---------------end--------------->8---

Adapting the formula as org-mode would automatically do if I typed enter
twice before the last hline is important, but updating the total value is
not (although nice), since I can do that with "C-u C-u C-c *" later when I
actually see the table.

After that the content of the file should be erased to prevent future
additions of the same information.

Any hints on how to do the different parts for this are welcome.

--
Darlan

Ps: I use the latest org-mode and Emacs versions (from git and bzr,
respectively) in a Linux box.


The motivation for all this is that I use org-mode tables to control my
expenses, but I want to be able to add new expenses from my android
phone. Using the "tasker" app (REALLY good) I could create a simple UI to
add the expense to a file that will be synced using Dropbox (one file for
each category, which corresponds to a different table). All of this is
working and now I the next step is the one described in this e-mail.