Question

I try to recognize the version of flexc++ program with regular expressions in CMake.

The ouput of flexc++ version is something like:

prompt$ flexc++ --version
flexc++ V1.01.00

I try to extract the version with regular expressions. The name of the executable is in a variable (and this variable is the output of other command). The problem is the string “++” in the flexc++ name. This string create a conflict with the symbol “+” (one or more matchs). A mini test:

set(sample "flexc++ V1.01.00")
set(flexname "flexc++")

string(REGEX REPLACE "^${flexname} V([0-9.]+)$" "\\1"
       output "${sample}")

message("${output}")

Throwing the next error:

RegularExpression::compile(): Nested *?+.
RegularExpression::compile(): Error in compile.
CMake Error at prueba.cmake:4 (string):
  string sub-command REGEX, mode REPLACE failed to compile regex "^flexc++
  V([0-9.]+)$".

If I erase the “++” string in sample and filename variables, it recognize perfect the version:

set(sample "flexc V1.01.00")
set(flexname "flexc")

string(REGEX REPLACE "^${flexname} V([0-9.]+)$" "\\1"
       output "${sample}")

message("${output}")

Output:

1.01.00

That means the problem is the “++” string.

How can I avoid this problem? For example, are there in CMake any command like:

scape(flexname_scaped ${flexname})

performing

flexname_scaped <-- flexc\\+\\+

?

How can I solve this problem?

Answer 1

You can escape the "++" using string(REPLACE...):

string(REPLACE "++" "\\+\\+" flexname_escaped ${flexname})
string(REGEX REPLACE "^${flexname_escaped} V([0-9.]+)$" "\\1"
       output "${sample}")