CMake: Looping through a string and getting the first three digits - makefile

Question

I'm trying to write a CMake script that does the following:
Using the execute_process instruction reads the output of a command and stores it into a variable named 'STRING_VARIABLE'. The command that returns something that has both characters and digits in it's name. Something like this: RESULT-v1.2.8-...
I have read this value properly and displayed it on the terminal to confirm this.
Now what I want to do is store the first three digits of this output and store them in 3 other variables: 'FIRST_DIGIT', 'SECOND_DIGIT' and 'THIRD_DIGIT'.
My logic was this:
Using a counter count each time a digit is encountered in a variable name. Each time a digit is encountered store the digit in one of the three variables then increment the counter. The counter counts therefore from 0 to 2 and for each of these 3 values does a store.
Here is the script I wrote:
SET(COUNTER 0)
foreach(LETTER ${STRING_VARIABLE})
if(LETTER EQUAL '0,1,2,3,4,5,6,7,8,9')
if( COUNTER EQUAL 0 ) # if first digit is encountered
list(GET STRING_VARIABLE LETTER FIRST_DIGIT) # store it in FIRST_DIGIT
SET(COUNTER 1)
elseif( COUNTER EQUAL 1 ) # if second digit is encountered
list(GET STRING_VARIABLE LETTER SECOND_DIGIT) # store it in SECOND_DIGIT
SET(COUNTER 2)
else( COUNTER EQUAL 2 ) # if second digit is encountered
list(GET STRING_VARIABLE LETTER THIRD_DIGIT) # store it in THIRD_DIGIT
endif()
endif()
endforeach()
# To check the variables
#message("*****${STRING_VARIABLE}") # OK!
message("*****${FIRST_DIGIT}") # NOT OK :(
As I'm a total beginner in CMake I suppose my problem is at either of the two(or both):
- When looping through the 'STRING_VARIABLE' I used foreach(LETTER) and since my string also contains digits the program may not see them. If that is the mistake with what else should I replace LETTER in order to get each character of the string?
- In the first if where I check if the 'LETTER' is a digit. I think that is the correct syntax altough I'm not sure. Basically what I'm doing there is trying to check if the letter at each index is a digit.
The 'STRING_VARIABLE' prints ok as I said.
However when I try printing the 'FIRST_DIGIT' or any other of the 3(second and third) I get an empty string as a result.
Please help me understand what is wrong in my logic and what I'm doing wrong.
Please help me understand what I'm doing wrong. Thank you.

Answer 1

In case the format is know, you can use string(REGEX REPLACE ...).
Function:
function(get_versions versionstring libname major minor patch)
string(REGEX REPLACE "([A-Za-z0-9_]*)-[vV].*" "\\1" locallibname ${versionstring} )
set(libname ${locallibname} PARENT_SCOPE)
string(REGEX REPLACE "^([A-Za-z0-9_]*-[vV])([0-9]*)([.][0-9]*[.][0-9]*-?.*)$" "\\2" numbers ${versionstring} )
set(major ${numbers} PARENT_SCOPE)
string(REGEX REPLACE "^([A-Za-z0-9_]*-[vV][0-9]*[.])([0-9]*)([.][0-9]*-?.*)$" "\\2" numbers ${versionstring} )
set(minor ${numbers} PARENT_SCOPE)
string(REGEX REPLACE "^([A-Za-z0-9_]*-[vV][0-9]*[.][0-9]*[.])([0-9]*)(-?.*)$" "\\2" numbers ${versionstring} )
set(patch ${numbers} PARENT_SCOPE)
endfunction()
Usage:
get_versions("MyLib-V11.222.034-remark" libname major minor patch)
status_ref(libname)
status_ref(major)
status_ref(minor)
status_ref(patch)
Result:
STATUS: libname = "MyLib"
STATUS: major = "11"
STATUS: minor = "222"
STATUS: patch = "034"