A target also has the ability to perform its execution if or unless a property has been set. This allows, for example, better control on the building process depending on the state of the system (OS, command-line property defines, etc.). To make a target sense this property, you should add the if or unless attribute with an expression that the target should react to. For example:
If no if and no unless attribute is present, the target will always be executed.
Note: the dependencies of a target are always executed before testing the target's condition."