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90 GNU make

$(and condition1[,condition2[,condition3...]])

The and function provides a “short-circuiting” AND operation. Each argument

is expanded, in order. If an argument expands to an empty string the processing

stops and the result of the expansion is the empty string. If all arguments

expand to a non-empty string then the result of the expansion is the expansion

of the last argument.

8.5 The foreach Function

The foreach function is very diﬀerent from other functions. It causes one piece of text to

be used repeatedly, each time with a diﬀerent substitution performed on it. It resembles

the for command in the shell sh and the foreach command in the C-shell csh.

The syntax of the foreach function is:

$(foreach var,list,text)

The ﬁrst two arguments, var and list, are expanded before anything else is done; note that

the last argument, text, is not expanded at the same time. Then for each word of the

expanded value of list, the variable named by the expanded value of var is set to that word,

and text is expanded. Presumably text contains references to that variable, so its expansion

will be diﬀerent each time.

The result is that text is expanded as many times as there are whitespace-separated

words in list. The multiple expansions of text are concatenated, with spaces between them,

to make the result of foreach.

This simple example sets the variable ‘files’ to the list of all ﬁles in the directories in

the list ‘dirs’:

dirs := a b c d

files := $(foreach dir,$(dirs),$(wildcard $(dir)/*))

Here text is ‘$(wildcard $(dir)/*)’. The ﬁrst repetition ﬁnds the value ‘a’ for dir, so

it produces the same result as ‘$(wildcard a/*)’; the second repetition produces the result

of ‘$(wildcard b/*)’; and the third, that of ‘$(wildcard c/*)’.

This example has the same result (except for setting ‘dirs’) as the following example:

files := $(wildcard a/* b/* c/* d/*)

When text is complicated, you can improve readability by giving it a name, with an

additional variable:

find_files = $(wildcard $(dir)/*)

dirs := a b c d

files := $(foreach dir,$(dirs),$(find_files))

Here we use the variable find_files this way. We use plain ‘=’ to deﬁne a recursively-

expanding variable, so that its value contains an actual function call to be re-expanded

under the control of foreach; a simply-expanded variable would not do, since wildcard

would be called only once at the time of deﬁning find_files.

The foreach function has no permanent eﬀect on the variable var; its value and ﬂavor

after the foreach function call are the same as they were beforehand. The other values

which are taken from list are in eﬀect only temporarily, during the execution of foreach.

The variable var is a simply-expanded variable during the execution of foreach. If var was

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