How to use the {n} syntax of regex with CMake

I have this string "2017-03-05-02-10-10_78205" and I want to match it with this pattern [0-9]{4}(-[0-9]{2}){5}_[0-9]+ but it doesn't work on CMake. See this example in CMake :

set(stuff "2017-03-05-02-10-10_78205")
if( "${stuff}" MATCHES "[0-9]{4}(-[0-9]{2}){5}_[0-9]+")
  message("Hello")
endif()

CMake doesn't seem to support the syntax {n}. Obviously, I solved my problem with that pattern [0-9-]+_[0-9]+

Nevertheless, I would like to know if I'm doing something wrong with the syntax {n}. Is it supported by CMake ? If not, how to define a specific number of repetition with CMake ?

I'm using an old CMake version (2.8.11.2).

Solution

We can get around this problem by using shell commands and execute_process. For instance, with echo and grep on linux :

set(stuff "2017-03-05-02-10-10_78205")
set(regexp "[0-9]{4}(-[0-9]{2}){5}_[0-9]+")
execute_process( COMMAND echo "${stuff}"
                 COMMAND grep -E -o "${regexp}"
                 OUTPUT_VARIABLE thing )
if(thing)
  message("Hello")
endif()

But we loose the cross-platform aspect of CMake.