4.1 Rule Example

Here is an example of a rule:

foo.o : foo.c defs.h       # module for twiddling the frobs
        cc -c -g foo.c

Its target is ‘foo.o’ and its prerequisites are ‘foo.c’ and ‘defs.h’. It has one command in the recipe: ‘cc -c -g foo.c’. The recipe starts with a tab to identify it as a recipe.

This rule says two things:

• How to decide whether ‘foo.o’ is out of date: it is out of date if it does not exist, or if either ‘foo.c’ or ‘defs.h’ is more recent than it.
• How to update the file ‘foo.o’: by running cc as stated. The recipe does not explicitly mention ‘defs.h’, but we presume that ‘foo.c’ includes it, and that that is why ‘defs.h’ was added to the prerequisites.

This document was generated by Davide Tacchella on November 3, 2010 using texi2html 1.82.