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Chapter 5: Writing Recipes in Rules 43

we will get output like this:

hello world

If you like, you can also use target-speciﬁc variables (see Section 6.11 [Target-speciﬁc

Variable Values], page 71) to obtain a tighter correspondence between the variable and the

recipe that uses it.

5.1.2 Using Variables in Recipes

The other way in which make processes recipes is by expanding any variable references in

them (see Section 6.1 [Reference], page 59). This occurs after make has ﬁnished reading

all the makeﬁles and the target is determined to be out of date; so, the recipes for targets

which are not rebuilt are never expanded.

Variable and function references in recipes have identical syntax and semantics to ref-

erences elsewhere in the makeﬁle. They also have the same quoting rules: if you want a

dollar sign to appear in your recipe, you must double it (‘$$’). For shells like the default

shell, that use dollar signs to introduce variables, it’s important to keep clear in your mind

whether the variable you want to reference is a make variable (use a single dollar sign) or a

shell variable (use two dollar signs). For example:

LIST = one two three

all:

for i in $(LIST); do \

echo $$i; \

done

results in the following command being passed to the shell:

for i in one two three; do \

echo $i; \

done

which generates the expected result:

one

two

three

5.2 Recipe Echoing

Normally make prints each line of the recipe before it is executed. We call this echoing

because it gives the appearance that you are typing the lines yourself.

When a line starts with ‘@’, the echoing of that line is suppressed. The ‘@’ is discarded

before the line is passed to the shell. Typically you would use this for a command whose

only eﬀect is to print something, such as an echo command to indicate progress through

the makeﬁle:

@echo About to make distribution files

When make is given the ﬂag ‘-n’ or ‘--just-print’ it only echoes most recipes, without

executing them. See Section 9.7 [Summary of Options], page 104. In this case even the

recipe lines starting with ‘@’ are printed. This ﬂag is useful for ﬁnding out which recipes

make thinks are necessary without actually doing them.

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