Porting from PL/SQL to PLPGSQL

Hi,

We are in the process of migrating of our application from Oracle to
PostGreSQL.


we are  facing a few problems with PL/SQL Code..

1)     In Exceptions ORACLE have something called WHEN OTHERS THEN cluase.I
can't find a replacement for that in            PostGreSQL.
2    Oracle have a function USERENV to get the user session
information.Is there any replacement available in PostGres. ?

3    Is there any replace available for INSTEAD OF INSERT/DELETE/UPDATE
for triggers in PostGreSQL.




Regards

Jomon Skariah.