Substitute of TRY and CATCH in postgres

Hi ,
We have a MSSQL proc which reads as below. We have to convert it to
Postgres using TRY CATCH. I googled about it and could not find significant
information. Can someone help?

SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO

CREATE PROCEDURE [SaveEmployeeOverview]
(
p_employeeNumber int,
p_dept char;
p_subdept;
)
AS
BEGIN
BEGIN TRY

IF EXISTS(
SELECT TOP 1 1 FROM employee WHERE employeenumber=p_employeenumber
)

BEGIN
UPDATE employee
SET dept=p_dept
subdept=p_subdept
WHERE employeenumber=(at)employeenumner

END

ELSE

BEGIN

INSERT INTO [dbo].[employee] (employeenumber , dept,subdept)
values(@p_employeenumber,@p_dept,@p_subdept)

END

SELECT Result = 1,
ErrorDesc =
''

RETURN 0

END TRY
BEGIN CATCH

SELECT Result = -1,
ErrorDesc =
ERROR_MESSAGE()
END CATCH
END

GO

Regards,
Aditya.