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8.4 Functions for Conditionals

There are four 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]) ¶

The 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…]]) ¶

The 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…]]) ¶

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.

$(intcmp lhs,rhs[,lt-part[,eq-part[,gt-part]]]) ¶

The intcmp function provides support for numerical comparison of integers. This function has no counterpart among the GNU make makefile conditionals.

The left-hand side, lhs, and right-hand side, rhs, are expanded and parsed as integral numbers in base 10. Expansion of the remaining arguments is controlled by how the numerical left-hand side compares to the numerical right-hand side.

If there are no further arguments, then the function expands to empty if the left-hand side and right-hand side do not compare equal, or to their numerical value if they do compare equal.

Else if the left-hand side is strictly less than the right-hand side, the intcmp function evaluates to the expansion of the third argument, lt-part. If both sides compare equal, then the intcmp function evaluates to the expansion of the fourth argument, eq-part. If the left-hand side is strictly greater than the right-hand side, then the intcmp function evaluates to the expansion of the fifth argument, gt-part.

If gt-part is missing, it defaults to eq-part. If eq-part is missing, it defaults to the empty string. Thus both ‘$(intcmp 9,7,hello)’ and ‘$(intcmp 9,7,hello,world,)’ evaluate to the empty string, while ‘$(intcmp 9,7,hello,world)’ (notice the absence of a comma after world) evaluates to ‘world’.