There are three functions that provide conditional expansion. A key aspect of these functions is that not all of the arguments are expanded initially. Only those arguments which need to be expanded, will be expanded.
$(if condition,then-part[,else-part])if function provides support for conditional expansion in a
functional context (as opposed to the GNU make makefile
conditionals such as ifeq (see Syntax of Conditionals).
The first argument, condition, first has all preceding and trailing whitespace stripped, then is expanded. If it expands to any non-empty string, then the condition is considered to be true. If it expands to an empty string, the condition is considered to be false.
If the condition is true then the second argument, then-part, is
evaluated and this is used as the result of the evaluation of the entire
if function.
If the condition is false then the third argument, else-part, is
evaluated and this is the result of the if function. If there is
no third argument, the if function evaluates to nothing (the
empty string).
Note that only one of the then-part or the else-part will be
evaluated, never both. Thus, either can contain side-effects (such as
shell function calls, etc.)
$(or condition1[,condition2[,condition3...]])or function provides a “short-circuiting” OR operation.
Each argument is expanded, in order. If an argument expands to a
non-empty string the processing stops and the result of the expansion
is that string. If, after all arguments are expanded, all of them are
false (empty), then the result of the expansion is the empty string.
$(and condition1[,condition2[,condition3...]])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.