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126 GNU make

A single-suﬃx rule is deﬁned by a single suﬃx, which is the source suﬃx. It matches

any ﬁle name, and the corresponding implicit prerequisite name is made by appending the

source suﬃx. A single-suﬃx rule whose source suﬃx is ‘.c’ is equivalent to the pattern rule

‘% : %.c’.

Suﬃx rule deﬁnitions are recognized by comparing each rule’s target against a deﬁned

list of known suﬃxes. When make sees a rule whose target is a known suﬃx, this rule is

considered a single-suﬃx rule. When make sees a rule whose target is two known suﬃxes

concatenated, this rule is taken as a double-suﬃx rule.

For example, ‘.c’ and ‘.o’ are both on the default list of known suﬃxes. Therefore,

if you deﬁne a rule whose target is ‘.c.o’, make takes it to be a double-suﬃx rule with

source suﬃx ‘.c’ and target suﬃx ‘.o’. Here is the old-fashioned way to deﬁne the rule for

compiling a C source ﬁle:

.c.o:

$(CC) -c $(CFLAGS) $(CPPFLAGS) -o $@ $<

Suﬃx rules cannot have any prerequisites of their own. If they have any, they are treated

as normal ﬁles with funny names, not as suﬃx rules. Thus, the rule:

.c.o: foo.h

$(CC) -c $(CFLAGS) $(CPPFLAGS) -o $@ $<

tells how to make the ﬁle .c.o from the prerequisite ﬁle foo.h, and is not at all like the

pattern rule:

%.o: %.c foo.h

$(CC) -c $(CFLAGS) $(CPPFLAGS) -o $@ $<

which tells how to make ‘.o’ ﬁles from ‘.c’ ﬁles, and makes all ‘.o’ ﬁles using this pattern

rule also depend on foo.h.

Suﬃx rules with no recipe are also meaningless. They do not remove previous rules as

do pattern rules with no recipe (see Section 10.5.6 [Canceling Implicit Rules], page 124).

They simply enter the suﬃx or pair of suﬃxes concatenated as a target in the data base.

The known suﬃxes are simply the names of the prerequisites of the special target

.SUFFIXES. You can add your own suﬃxes by writing a rule for .SUFFIXES that adds

more prerequisites, as in:

.SUFFIXES: .hack .win

which adds ‘.hack’ and ‘.win’ to the end of the list of suﬃxes.

If you wish to eliminate the default known suﬃxes instead of just adding to them, write

a rule for .SUFFIXES with no prerequisites. By special dispensation, this eliminates all

existing prerequisites of .SUFFIXES. You can then write another rule to add the suﬃxes

you want. For example,

.SUFFIXES: # Delete the default suﬃxes

.SUFFIXES: .c .o .h # Deﬁne our suﬃx list

The ‘-r’ or ‘--no-builtin-rules’ ﬂag causes the default list of suﬃxes to be empty.

The variable SUFFIXES is deﬁned to the default list of suﬃxes before make reads any

makeﬁles. You can change the list of suﬃxes with a rule for the special target .SUFFIXES,

but that does not alter this variable.

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