[O] Macro and babel

[tony day]

I had written this:

,----
| #+MACRO: testdir ~/working
| #+begin_src sh
|   cd  {{{testdir}}}
| #+end_src
`----

Thinking it would do this:

,----
| #+begin_src sh
|   cd ~/working
| #+end_src
`----
Alas, #+Macro acts on export only.
 
Is there a quick way to effect general text substitution on C-c C-c?  That 
would be an awesome feature, basically adding macro capabilities to every 
babelable language.  Or am I missing something?


Tony