[CMake] What does this mean: IF("${VARIABLE}" MATCHES "^${VARIABLE}$")

[Bill Hoffman]

Jian Wang wrote:

>     Why is IF("${VARIABLE}" MATCHES "^${VARIABLE}$") used instead of IF(
>     ${VARIABLE} STREQUAL ${VARIABLE} ) (which would always return true)?
>     I'm not sure of use case but I'd say it's checking for special
>     characters in VARIABLE.
> 
> If it's checking for special characters then I have to say that it's not 
> the right way. For example, if VARIABLE == "a/b" then the IF statement 
> is still TRUE.

It is checking to see if the VARIABLE has a value at all.  It is old 
code before we had IF(DEFINED VARIABLE) but works with all versions of 
CMake.

-Bill