Code from Figure 15 of “Enable Your Process Chains to React to Outcomes of ABAP Programs” by David Eady.

*&---------------------------------------------------------------------*
*& Report  ZBW_CHKFIRSTDAYOFPERIOD                                     *
*&                                                                     *
*&---------------------------------------------------------------------*
*&                                                                     *
*&                                                                     *
*&---------------------------------------------------------------------*

REPORT  ZBW_CHKFIRSTDAYOFPERIOD                 .

************************************************************************
* Date: 5/3/2005
* Author: David Eady
*
* This program is intended to be called by BW process chains. It should
* check if today is the first day of the fiscal period. If so, it
* should do nothing (complete successfully). If not it should
* return message ZBW 003 as an error. This should terminate process
* chain execution.
*



data: wfirstday like sy-datum.
data: wbuper like t009b-poper.
data: wgjahr like t009b-bdatj.

* get today's fiscal period
CALL FUNCTION 'DATE_TO_PERIOD_CONVERT'
  EXPORTING
    I_DATE               = sy-datum
*   I_MONMIT             = 00
    I_PERIV              = 'V9'
  IMPORTING
    E_BUPER              = wbuper
    E_GJAHR              = wgjahr
  EXCEPTIONS
    INPUT_FALSE          = 1
    T009_NOTFOUND        = 2
    T009B_NOTFOUND       = 3
    OTHERS               = 4.

* get the first day of the period
CALL FUNCTION 'FIRST_DAY_IN_PERIOD_GET'
  EXPORTING
    I_GJAHR              = wgjahr
*   I_MONMIT             = 00
    I_PERIV              = 'V9'
    I_POPER              = wbuper
  IMPORTING
    E_DATE               = wfirstday
  EXCEPTIONS
    INPUT_FALSE          = 1
    T009_NOTFOUND        = 2
    T009B_NOTFOUND       = 3
    OTHERS               = 4.

* if today is not the first day of the period, return an error.
if sy-datum <> wfirstday.

* Date is not the first day of the fiscal period.
  MESSAGE E003(ZBW).

endif.

* otherwise complete successfully