You can use a special syntax to test for the existence of macros. For example:

%{?macro_to_test: expression}

This syntax tells RPM to expand the expression if macro_to_test exists, otherwise ignore. A leading exclamation point, !, tests for the non-existence of a macro:

%{!?macro_to_test: expression}

In this example, if the macro_to_test macro does not exist, then expand the expression.

The %if macro performs an if test much like scripting languages. For example:

%if %{old_5x}

%define b5x 1

%undefine b6x

%endif

A %else allows you to specify what to do if the test is not successful. For example:

%if %{old_5x}

%define b5x 1

%undefine b6x

%else

%define b6x 1

%undefine b5x

%endif

Again, use an exclamation point to negate the test. For example:

%if ! %{old_5x}

%define b5x 1

%undefine b6x

%endif

You can use a && for an and test. For example:

%if %{old_5x} && %{old_6x}

%{error: You cannot build for .5x and .6x at the same time}

%quit

%endif