Roland Ver. 4.5 Technické informace stáhnout pdf (Strana 129)

Chapter 10: Using Implicit Rules 119

Thus, a pattern rule ‘%.o : %.c’ says how to make any ﬁle stem.o from another ﬁle

stem.c.

Note that expansion using ‘%’ in pattern rules occurs after any variable or function ex-

pansions, which take place when the makeﬁle is read. See Chapter 6 [How to Use Variables],

page 59, and Chapter 8 [Functions for Transforming Text], page 83.

10.5.1 Introduction to Pattern Rules

A pattern rule contains the character ‘%’ (exactly one of them) in the target; otherwise, it

looks exactly like an ordinary rule. The target is a pattern for matching ﬁle names; the ‘%’

matches any nonempty substring, while other characters match only themselves.

For example, ‘%.c’ as a pattern matches any ﬁle name that ends in ‘.c’. ‘s.%.c’ as

a pattern matches any ﬁle name that starts with ‘s.’, ends in ‘.c’ and is at least ﬁve

characters long. (There must be at least one character to match the ‘%’.) The substring

that the ‘%’ matches is called the stem.

‘%’ in a prerequisite of a pattern rule stands for the same stem that was matched by the

‘%’ in the target. In order for the pattern rule to apply, its target pattern must match the

ﬁle name under consideration and all of its prerequisites (after pattern substitution) must

name ﬁles that exist or can be made. These ﬁles become prerequisites of the target.

Thus, a rule of the form

%.o : %.c ; recipe...

speciﬁes how to make a ﬁle n.o, with another ﬁle n.c as its prerequisite, provided that n .c

exists or can be made.

There may also be prerequisites that do not use ‘%’; such a prerequisite attaches to every

ﬁle made by this pattern rule. These unvarying prerequisites are useful occasionally.

A pattern rule need not have any prerequisites that contain ‘%’, or in fact any prerequi-

sites at all. Such a rule is eﬀectively a general wildcard. It provides a way to make any ﬁle

that matches the target pattern. See

Section 10.6 [Last Resort], page 125.

More than one pattern rule may match a target. In this case make will choose the “best

ﬁt” rule. See Section 10.5.4 [How Patterns Match], page 122.

Pattern rules may have more than one target. Unlike normal rules, this does not act as

many diﬀerent rules with the same prerequisites and recipe. If a pattern rule has multiple

targets, make knows that the rule’s recipe is responsible for making all of the targets. The

recipe is executed only once to make all the targets. When searching for a pattern rule to

match a target, the target patterns of a rule other than the one that matches the target in

need of a rule are incidental: make worries only about giving a recipe and prerequisites to

the ﬁle presently in question. However, when this ﬁle’s recipe is run, the other targets are

marked as having been updated themselves.

10.5.2 Pattern Rule Examples

Here are some examples of pattern rules actually predeﬁned in make. First, the rule that

compiles ‘.c’ ﬁles into ‘.o’ ﬁles:

%.o : %.c

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

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