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These macros check for the presence or behavior of particular programs. They are used to choose between several alternative programs and to decide what to do once one has been chosen. If there is no macro specifically defined to check for a program you need, and you don't need to check for any special properties of it, then you can use one of the general program-check macros.
5.2.1 Particular Program Checks Special handling to find certain programs 5.2.2 Generic Program and File Checks How to find other programs