[ABAP] Erster Tag des aktuellen Monats berechnen

* Variante 1 (cl_bs_period_toolset_basics)
DATA(lv_first_day) = cl_bs_period_toolset_basics=>get_first_day_in_month( iv_date = sy-datum ).

* Variante 2 (cl_hrpad_date_computations)
DATA(lv_first_day) = cl_hrpad_date_computations=>get_last_day_previous_month( sy-datum ) + 1.