make uses an internal table of rules to learn how to transform a file with one suffix into a file with another suffix. If the -r flag is used on the make command line, the internal table is not used.
The list of suffixes is actually the dependency list for the name .SUFFIXES. make searches for a file with any of the suffixes on the list. If it finds one, make transforms it into a file with another suffix. Transformation rule names are the concatenation of the before and after suffixes. The name of the rule to transform a .r file to a .o file is thus .r.o. If the rule is present and no explicit command sequence has been given in the user's description files, the command sequence for the rule .r.o is used. If a command is generated by using one of these suffixing rules, the macro $ is given the value of the stem (everything but the suffix) of the name of the file to be made; and the macro $< is the full name of the dependent that caused the action.
The order of the suffix list is significant since the list is scanned from
left to right.
The first name formed that has both a file
and a rule associated with it is used.
If new names are to be appended, the user can add an entry for
.SUFFIXES in the description file. The dependents are added to the usual list.
A .SUFFIXES line without any dependents deletes the current list. It is necessary to clear the current list if the order of names is to be changed.