8.1 Function Call Syntax
A function call resembles a variable reference. It looks like this:
or like this:
Here function is a function name; one of a short list of names
that are part of make. You can also essentially create your own
functions by using the call builtin function.
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
parentheses 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 this:
| | 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.
