Make/Value-Function
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8.8 The value
Function
The value
function provides a way for you to use the value of a
variable without having it expanded. Please note that this
does not undo expansions which have already occurred; for example if
you create a simply expanded variable its value is expanded during the
definition; in that case the value
function will return the
same result as using the variable directly.
The syntax of the value
function is:
$(value variable)
Note that variable
is the name of a variable, not a
reference to that variable. Therefore you would not normally
use a ā$
ā or parentheses when writing it. (You can, however, use
a variable reference in the name if you want the name not to be a
constant.)
The result of this function is a string containing the value of
variable
, without any expansion occurring. For example, in this
makefile:
FOO = $PATH all: @echo $(FOO) @echo $(value FOO)
The first output line would be ATH
, since the ā$Pā would be
expanded as a make
variable, while the second output line would
be the current value of your $PATH
environment variable, since
the value
function avoided the expansion.
The value
function is most often used in conjunction with the
eval
function (see Eval Function).