set term ^;
-- zap if dependencies exists:
create or alter procedure sp_check_ctx as begin end^ 
create or alter procedure sp_main as begin end^
set term ;^
commit;

recreate exception
    required_context_var_not_found
    'required context variable ''@1'' not found in namespace ''@2''';
commit;

set term ^;
create or alter procedure sp_check_ctx(
  ctx_nmspace_01 varchar(20),
  ctx_varname_01 varchar(80)
)
as
begin
  if ( rdb$get_context( upper(ctx_nmspace_01), upper(ctx_varname_01) ) is null  ) then
    exception required_context_var_not_found using( upper(ctx_varname_01), upper(ctx_nmspace_01) );
end^

create or alter procedure sp_main returns (dts timestamp) as
begin
  execute procedure sp_check_ctx('USER_SESSION','SOME_UNKNOWN_VAR');
  dts = current_timestamp;
  suspend;
end

^set term ;^
commit;

$ /opt/fb30trnk/bin/isql localhost/3333:test30
Database:  localhost/3333:test30
SQL> select * from sp_main;

                      DTS
=========================
Statement failed, SQLSTATE = HY000
exception 10
-REQUIRED_CONTEXT_VAR_NOT_FOUND
-required context variable ' SOME_UNKNOWN_VAR ' not found in namespace ' USER_SESSION '

REQUIRED_CONTEXT_VAR_NOT_FOUND.
unknown ISC error 335545016.

REQUIRED_CONTEXT_VAR_NOT_FOUND.
required context variable 'SOME_UNKNOWN_VAR' not found in namespace 'USER_SESSION'.