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Chapter 4: Writing Rules 37

objects = foo.o bar.o

all: $(objects)

$(objects): %.o: %.c

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

Here ‘$<’ is the automatic variable that holds the name of the prerequisite and ‘$@’ is

the automatic variable that holds the name of the target; see Section 10.5.3 [Automatic

Variables], page 120.

Each target speciﬁed must match the target pattern; a warning is issued for each target

that does not. If you have a list of ﬁles, only some of which will match the pattern, you can

use the filter function to remove non-matching ﬁle names (see Section 8.2 [Functions for

String Substitution and Analysis], page 84):

files = foo.elc bar.o lose.o

$(filter %.o,$(files)): %.o: %.c

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

$(filter %.elc,$(files)): %.elc: %.el

emacs -f batch-byte-compile $<

In this example the result of ‘$(filter %.o,$(files))’ is bar.o lose.o , and the ﬁrst static

pattern rule causes each of these object ﬁles to be updated by compiling the corresponding

C source ﬁle. The result of ‘$(filter %.elc,$(files))’ is foo.elc, so that ﬁle is made

from foo.el.

Another example shows how to use $* in static pattern rules:

bigoutput littleoutput : %output : text.g

generate text.g -$* > $@

When the generate command is run, $* will expand to the stem, either ‘big’ or ‘little’.

4.11.2 Static Pattern Rules versus Implicit Rules

A static pattern rule has much in common with an implicit rule deﬁned as a pattern rule

(see Section 10.5 [Deﬁning and Redeﬁning Pattern Rules], page 118). Both have a pattern

for the target and patterns for constructing the names of prerequisites. The diﬀerence is in

how make decides when the rule applies.

An implicit rule can apply to any target that matches its pattern, but it does apply

only when the target has no recipe otherwise speciﬁed, and only when the prerequisites can

be found. If more than one implicit rule appears applicable, only one applies; the choice

depends on the order of rules.

By contrast, a static pattern rule applies to the precise list of targets that you specify

in the rule. It cannot apply to any other target and it invariably does apply to each of the

targets speciﬁed. If two conﬂicting rules apply, and both have recipes, that’s an error.

The static pattern rule can be better than an implicit rule for these reasons:

• You may wish to override the usual implicit rule for a few ﬁles whose names cannot be

categorized syntactically but can be given in an explicit list.

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Roland Ver. 4.5 Technical Information Seite 47