ifneq

ifneq is a directive used in build systems, most notably in Makefiles. It is a conditional directive that allows a build process to execute certain commands or define variables only if two strings are not equal. The syntax typically involves the keyword ifneq followed by two arguments, which are the strings to be compared. If the first string is not equal to the second string, the commands or definitions between the ifneq directive and its corresponding endif directive are processed.

This directive is crucial for controlling the flow of build processes based on varying conditions. For instance, it can be used to check if a particular configuration option is not set to a default value, or if a variable contains a different string than expected. This allows for flexible build configurations and the ability to adapt to different environments or user preferences without modifying the core Makefile. The comparison is case-sensitive.

The counterpart to ifneq is the ifeq directive, which executes commands or defines variables when the two strings are equal. Together, ifeq and ifneq provide a robust mechanism for creating conditional logic within Makefiles, enabling sophisticated and adaptable build automation. The ifneq directive is terminated by an endif directive, which marks the end of the conditional block.