CMAKE_MINIMUM_REQUIRED(VERSION 2.8 FATAL_ERROR)
PROJECT(STREQUAL NONE)
SET(CMAKE_VERBOSE_MAKEFILE ON)

UNSET(NONEXIST)
UNSET(NONEXIST CACHE)
IF(NONEXIST STREQUAL "xyz")
    MESSAGE("STREQUAL, NONEXIST[SCOPE]=${NONEXIST}, NONEXIST[CACHE]=$CACHE{NONEXIST}")
ELSE()
    MESSAGE("NOT STREQUAL, NONEXIST[SCOPE]=${NONEXIST}, NONEXIST[CACHE]=$CACHE{NONEXIST}")
ENDIF()

SET(SCOPEONLY "xyz")
UNSET(SCOPEONLY CACHE)
IF(SCOPEONLY STREQUAL "xyz")
    MESSAGE("STREQUAL, SCOPEONLY[SCOPE]=${SCOPEONLY}, SCOPEONLY[CACHE]=$CACHE{SCOPEONLY}")
ELSE()
    MESSAGE("NOT STREQUAL, SCOPEONLY[SCOPE]=${SCOPEONLY}, SCOPEONLY[CACHE]=$CACHE{SCOPEONLY}")
ENDIF()

SET(CACHEONLY "xyz" CACHE STRING "" FORCE)
SET(CACHEONLY "pqr")  # In order to check if UNSET(CACHEONLY) really...
UNSET(CACHEONLY)      # ...unsets CACHEONLY only in the current scope.
IF(CACHEONLY STREQUAL "xyz")
    MESSAGE("STREQUAL, CACHEONLY[SCOPE]=${CACHEONLY}, CACHEONLY[CACHE]=$CACHE{CACHEONLY}")
ELSE()
    MESSAGE("NOT STREQUAL, CACHEONLY[SCOPE]=${CACHEONLY}, CACHEONLY[CACHE]=$CACHE{CACHEONLY}")
ENDIF()

SET(BOTHEQUAL "xyz" CACHE STRING "" FORCE)
SET(BOTHEQUAL "xyz")  # Actually unnecessary.
IF(BOTHEQUAL STREQUAL "xyz")
    MESSAGE("STREQUAL, BOTHEQUAL[SCOPE]=${BOTHEQUAL}, BOTHEQUAL[CACHE]=$CACHE{BOTHEQUAL}")
ELSE()
    MESSAGE("NOT STREQUAL, BOTHEQUAL[SCOPE]=${BOTHEQUAL}, BOTHEQUAL[CACHE]=$CACHE{BOTHEQUAL}")
ENDIF()

SET(BOTHUNEQUAL "abc" CACHE STRING "" FORCE)
SET(BOTHUNEQUAL "xyz")
IF(BOTHUNEQUAL STREQUAL "xyz")
    MESSAGE("STREQUAL, BOTHUNEQUAL[SCOPE]=${BOTHUNEQUAL}, BOTHUNEQUAL[CACHE]=$CACHE{BOTHUNEQUAL}")
ELSE()
    MESSAGE("NOT STREQUAL, BOTHUNEQUAL[SCOPE]=${BOTHUNEQUAL}, BOTHUNEQUAL[CACHE]=$CACHE{BOTHUNEQUAL}")
ENDIF()