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Defining Conditional Builds

With the ability to define macros inside spec files, and also to use macros defined elsewhere, you gain a lot of control over how your package gets built. You can go further, though, and use special directives to perform only certain commands based on certain conditions. This adds a powerful capability to your spec files, and also makes it much easier to do things like build for multiple versions of Linux or other operating systems, as well as handle various backwards-compatibility issues.
To define conditional build commands, you need to create conditional constructs in your package’s spec file. In addition, you need to define macros that the conditional constructs use to determine whether or not to execute a set of spec file directives.
Cross Reference
See Chapter 20, Customizing RPM Behavior for more on macro file locations, and Chapter 18, Using RPM on Non-Red Hat Linuxes and Chapter 19, RPM on Other Operating Systems for more on using RPM on other versions of Linux and other operating systems, respectively.
RPM supports a number of ways to make parts of your spec file enabled or disabled based on certain conditions. These include conditional macros, conditional blocks, and special directives based on the system architecture.

Defining conditional macros

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 the macro macro_to_test exists. If the macro macro_to_test does not exist, nothing will be output. You can also reverse this test. 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, RPM will expand the expression.
If you want, you can omit the expression and just test for the existence of the macro. If it exists, RPM will use the value of the macro. If the macro does not exist, RPM will use nothing. For example:
./configure %{?_with_ldap}
In this case, if the _with_ldap macro exists, the value of that macro will get passed on the command line to the configure script. If the _with_ldap macro does not exist, nothing extra will be passed on the command line to the configure script. This is very important when creating commands to build or install packages.
Cross Reference
Many of the macros you will test this way are set up with the --with command-line parameter. See Chapter 18, Using RPM on Non-Red Hat Linuxes for details.