[trigger] is it possible to launch a shell script?

Hello all,

I have to synchronize the content of 2 databases, each one being used by an
application from our Information System ; unfortunately these apps require a
specific DBMS : one needs MySQL and the other Postgresql.
Now I want the mysql database to be updated with the data from Postgresql
when this one is updated itself.

I heard about triggers, but I did not find any way to activate something
else than an SQL procedure with Postgresql ; with Oracle I know that I can
launch nearly whatever I want (including standalone sowtware) and I can
easily write a shell script which would call the mysql & insert the data,
BUT is it possible at all?

Thank you in advance for your answers, remarks and suggestions.

Faithfully yours,
Grégory Luguet