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Function Call Syntax
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Function Call Syntax
A function call resembles a variable reference.
It looks like:
$(function arguments); or like: ${function arguments}.
In the previous example,
function is a function name; one of a short list of names that are part of make. There is no provision for defining new functions.
The
arguments are the arguments of the function. They are separated from the function name
by one or more spaces or tabs, and if there is more than one argument, then
they are separated by commas. Such whitespace and commas are not part of an
argument’s value. The delimiters which you use to surround the function call, whether
paren-theses or braces, can appear in an argument only in matching pairs; the
other kind of delimiters may appear singly. If the arguments themselves contain
other function calls or variable references, it is wisest to use the same kind
of delimiters for all the references; write ‘$(subst a,b,$(x))’, not ‘$(subst a,b,${x})’. This is because it is clearer, and because only one type of delimiter is
matched to find the end of the reference.
The text written for each argument is processed by substitution of variables
and function calls to produce the argument value, which is the text on which the
function acts. The substitution is done in the order in which the arguments
appear.
Commas and unmatched parentheses or braces cannot appear in the text of an
argument as written; leading spaces cannot appear in the text of the first
argument as written. These characters can be put into the argument value by variable
substitution. First define variables
comma and space whose values are isolated comma and space characters; then, substitute these
variables where such characters are wanted, like the following example shows.
comma:= ,
empty:=
space:= $(empty) $(empty)
foo:= a b c
bar:= $(subst $(space),$(comma),$(foo))
# bar is now ‘a,b,c’.
Here the subst function replaces each space with a comma, through the value of foo, and substitutes the result.
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