ifeq

ifeq is a conditional directive used in GNU Makefiles to evaluate whether two strings are equal after variable expansion. When the condition is true, the makefile region following the directive up to the matching else or endif is included in the build; otherwise that region is skipped.

Syntax: ifeq (arg1, arg2) ... else ... endif. The two arguments are expanded before comparison, and whitespace around the comma is ignored. Strings are compared exactly as expanded; there is no built‑in numeric comparison. To compare numbers, you typically convert them to strings or use a shell construct within the Makefile if needed.

Examples: ifeq ($(CC),gcc)

CC_IS_GCC := 1

else

CC_IS_GCC := 0

endif

You can test for empty values with ifeq ($(strip $(VAR)),). The strip function removes surrounding whitespace from VAR before the comparison, which is a common technique to avoid false negatives due to formatting.

Notes: ifeq is one of several conditional directives in GNU Make, alongside ifneq, ifdef, and ifndef. It is specific to GNU Make and may not be portable to all non‑GNU make implementations. Conditions can be nested with else and endif, and variables or functions can be used within the arguments to drive build logic, such as platform selection, feature flags, or toolchain choices.

See also: GNU make, conditional syntax, ifneq, ifdef, else, endif.