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Chapter 4: Writing Rules 21

4 Writing Rules

A rule appears in the makeﬁle and says when and how to remake certain ﬁles, called the

rule’s targets (most often only one per rule). It lists the other ﬁles that are the prerequisites

of the target, and the recipe to use to create or update the target.

The order of rules is not signiﬁcant, except for determining the default goal: the target

for make to consider, if you do not otherwise specify one. The default goal is the target of

the ﬁrst rule in the ﬁrst makeﬁle. If the ﬁrst rule has multiple targets, only the ﬁrst target

is taken as the default. There are two exceptions: a target starting with a period is not

a default unless it contains one or more slashes, ‘/’, as well; and, a target that deﬁnes a

pattern rule has no eﬀect on the default goal. (See Section 10.5 [Deﬁning and Redeﬁning

Pattern Rules], page 118.)

Therefore, we usually write the makeﬁle so that the ﬁrst rule is the one for compiling

the entire program or all the programs described by the makeﬁle (often with a target called

‘all’). See Section 9.2 [Arguments to Specify the Goals], page 99.

4.1 Rule Syntax

In general, a rule looks like this:

targets : prerequisites

recipe

...

or like this:

targets : prerequisites ; recipe

recipe

...

The targets are ﬁle names, separated by spaces. Wildcard characters may be used (see

Section 4.3 [Using Wildcard Characters in File Names], page 23) and a name of the form

a(m) represents member m in archive ﬁle a (see Section 11.1 [Archive Members as Targets],

page 129). Usually there is only one target per rule, but occasionally there is a reason to

have more (see Section 4.9 [Multiple Targets in a Rule], page 34).

The recipe lines start with a tab character (or the ﬁrst character in the value of the

.RECIPEPREFIX variable; see Section 6.14 [Special Variables], page 73). The ﬁrst recipe line

may appear on the line after the prerequisites, with a tab character, or may appear on the

same line, with a semicolon. Either way, the eﬀect is the same. There are other diﬀerences

in the syntax of recipes. See Chapter 5 [Writing Recipes in Rules], page 41.

Because dollar signs are used to start make variable references, if you really want a dollar

Variables], page 59). If you have enabled secondary expansion (see Section 3.8 [Secondary

Expansion], page 18) and you want a literal dollar sign in the prerequisites list, you must

actually write four dollar signs (‘$$$$’).

You may split a long line by inserting a backslash followed by a newline, but this is not

required, as make places no limit on the length of a line in a makeﬁle.

A rule tells make two things: when the targets are out of date, and how to update them

when necessary.

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Roland Ver. 4.5 Informacje Techniczne Strona 31