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Chapter 5: Writing Recipes in Rules 41

5 Writing Recipes in Rules

The recipe of a rule consists of one or more shell command lines to be executed, one at a

time, in the order they appear. Typically, the result of executing these commands is that

the target of the rule is brought up to date.

Users use many diﬀerent shell programs, but recipes in makeﬁles are always interpreted

by /bin/sh unless the makeﬁle speciﬁes otherwise. See Section 5.3 [Recipe Execution],

page 44.

5.1 Recipe Syntax

Makeﬁles have the unusual property that there are really two distinct syntaxes in one

ﬁle. Most of the makeﬁle uses make syntax (see Chapter 3 [Writing Makeﬁles], page 11).

However, recipes are meant to be interpreted by the shell and so they are written using

shell syntax. The make program does not try to understand shell syntax: it performs only

a very few speciﬁc translations on the content of the recipe before handing it to the shell.

Each line in the recipe must start with a tab (or the ﬁrst character in the value of the

.RECIPEPREFIX variable; see

Section 6.14 [Special Variables], page 73), except that the ﬁrst

recipe line may be attached to the target-and-prerequisites line with a semicolon in between.

Any line in the makeﬁle that begins with a tab and appears in a “rule context” (that is,

after a rule has been started until another rule or variable deﬁnition) will be considered

part of a recipe for that rule. Blank lines and lines of just comments may appear among

the recipe lines; they are ignored.

Some consequences of these rules include:

• A blank line that begins with a tab is not blank: it’s an empty recipe (see Section 5.9

[Empty Recipes], page 57).

• A comment in a recipe is not a make comment; it will be passed to the shell as-is.

Whether the shell treats it as a comment or not depends on your shell.

• A variable deﬁnition in a “rule context” which is indented by a tab as the ﬁrst character

on the line, will be considered part of a recipe, not a make variable deﬁnition, and passed

to the shell.

• A conditional expression (ifdef, ifeq, etc. see Section 7.2 [Syntax of Conditionals],

page 78) in a “rule context” which is indented by a tab as the ﬁrst character on the

line, will be considered part of a recipe and be passed to the shell.

5.1.1 Splitting Recipe Lines

One of the few ways in which make does interpret recipes is checking for a backslash just

before the newline. As in normal makeﬁle syntax, a single logical recipe line can be split

into multiple physical lines in the makeﬁle by placing a backslash before each newline. A

sequence of lines like this is considered a single recipe line, and one instance of the shell will

be invoked to run it.

However, in contrast to how they are treated in other places in a makeﬁle (see

Section 3.1.1 [Splitting Long Lines], page 12), backslash/newline pairs are not removed

from the recipe. Both the backslash and the newline characters are preserved and passed

to the shell. How the backslash/newline is interpreted depends on your shell. If the ﬁrst

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