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112 GNU make

ﬁles are supposed to exist. See Section 10.2 [Catalogue of Built-In Rules], page 112, for a

catalogue of all the predeﬁned implicit rules.

Above, we said an implicit rule applies if the required prerequisites “exist or can be

made”. A ﬁle “can be made” if it is mentioned explicitly in the makeﬁle as a target or a

prerequisite, or if an implicit rule can be recursively found for how to make it. When an

implicit prerequisite is the result of another implicit rule, we say that chaining is occurring.

See Section 10.4 [Chains of Implicit Rules], page 117.

In general, make searches for an implicit rule for each target, and for each double-colon

rule, that has no recipe. A ﬁle that is mentioned only as a prerequisite is considered a

target whose rule speciﬁes nothing, so implicit rule search happens for it. See Section 10.8

[Implicit Rule Search Algorithm], page 127, for the details of how the search is done.

Note that explicit prerequisites do not inﬂuence implicit rule search. For example, con-

sider this explicit rule:

foo.o: foo.p

The prerequisite on foo.p does not necessarily mean that make will remake foo.o according

to the implicit rule to make an object ﬁle, a .o ﬁle, from a Pascal source ﬁle, a .p ﬁle. For

example, if foo.c also exists, the implicit rule to make an object ﬁle from a C source ﬁle

is used instead, because it appears before the Pascal rule in the list of predeﬁned implicit

rules (see Section 10.2 [Catalogue of Built-In Rules], page 112).

If you do not want an implicit rule to be used for a target that has no recipe, you can

give that target an empty recipe by writing a semicolon (see Section 5.9 [Deﬁning Empty

Recipes], page 57).

10.2 Catalogue of Built-In Rules

Here is a catalogue of predeﬁned implicit rules which are always available unless the

makeﬁle explicitly overrides or cancels them. See Section 10.5.6 [Canceling Implicit

Rules], page 124, for information on canceling or overriding an implicit rule. The ‘-r’ or

‘--no-builtin-rules’ option cancels all predeﬁned rules.

This manual only documents the default rules available on POSIX-based operating sys-

tems. Other operating systems, such as VMS, Windows, OS/2, etc. may have diﬀerent sets

of default rules. To see the full list of default rules and variables available in your version

of GNU make, run ‘make -p’ in a directory with no makeﬁle.

Not all of these rules will always be deﬁned, even when the ‘-r’ option is not given.

Many of the predeﬁned implicit rules are implemented in make as suﬃx rules, so which

ones will be deﬁned depends on the suﬃx list (the list of prerequisites of the special target

.SUFFIXES). The default suﬃx list is: .out, .a, .ln, .o, .c, .cc, .C, .cpp, .p, .f, .F, .m,

.r, .y, .l, .ym, .lm, .s, .S, .mod, .sym, .def, .h, .info, .dvi, .tex, .texinfo, .texi,

.txinfo, .w, .ch .web, .sh, .elc, .el. All of the implicit rules described below whose

prerequisites have one of these suﬃxes are actually suﬃx rules. If you modify the suﬃx list,

the only predeﬁned suﬃx rules in eﬀect will be those named by one or two of the suﬃxes

that are on the list you specify; rules whose suﬃxes fail to be on the list are disabled. See

Section 10.7 [Old-Fashioned Suﬃx Rules], page 125, for full details on suﬃx rules.

Compiling C programs

n.o is made automatically from n.c with a recipe of the form ‘$(CC)

$(CPPFLAGS) $(CFLAGS) -c’.

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