How to call a bash script from cmake and pass a generator dependent string as argument? - cmake

Question

While using the Unix Makefiles generator I have added the following to a CMakeLists.txt file:
add_custom_target(maintainer-clean
# The current directory is CMAKE_CURRENT_BINARY_DIR.
COMMAND ${CMAKE_CURRENT_SOURCE_DIR}/cwm4/scripts/cmake_maintainer_clean.sh $(MAKE) \"${GITACHE_PACKAGES}\"
)
This cmake_maintainer_clean.sh script is make specific, and it needs to use $(MAKE) in the generated Makefile when calling the script.
However, when switching to the generator Ninja this custom command is put as-is in the build.ninja file, causing the $ of the $(MAKE) to cause problems (ninja refuses to run any target, failing to parse build.ninja).
Therefore, I wish to make this generator-specific. How can I use $(MAKE) as first argument to the script when the generator is Unix Makefiles and something else, without a $ - e.g. "ninja" - when the generator is Ninja?
Can I do something like:
COMMAND ${CMAKE_CURRENT_SOURCE_DIR}/cwm4/scripts/cmake_maintainer_clean.sh $<UNIX:$(MAKE),ninja> \"${GITACHE_PACKAGES}\"
?

Answer 1

I would make separate presets for each generator, so you can associate a particular environment variable with it. Here is how the CMakePresets.json file may look like:
{
"version": 2,
"cmakeMinimumRequired": {
"major": 3,
"minor": 20,
"patch": 0
},
"configurePresets": [
{
"name": "base",
"binaryDir": "${sourceDir}/build",
"hidden": true
},
{
"name": "Ninja",
"inherits": "base",
"displayName": "Ninja Config",
"generator": "Ninja",
"environment": {
"SCRIPT_ARG": "Ninja"
}
},
{
"name": "Make",
"inherits": "base",
"displayName": "Make Config",
"generator": "Unix Makefiles",
"environment": {
"SCRIPT_ARG": "Make"
}
}
]
}
Where the SCRIPT_ARG can be read later inside of the CMakeLists.txt configuration:
cmake_minimum_required(VERSION 3.20)
project(Hello)
add_executable(Hello main.cpp)
add_custom_target(my-script
COMMAND ${CMAKE_CURRENT_SOURCE_DIR}/script.sh $ENV{SCRIPT_ARG}
)
add_dependencies(Hello my-script)
Providing script.sh is as simple as this:
#!/bin/sh
echo "Hello from script, $1!"
You will end up with the following output during build phase:
% cmake --preset Make
...
% cmake --build build
Hello from script, Make!
[ 0%] Built target my-script
...
Corresponding output for Ninja generator would be:
% cmake --preset Ninja
...
% cmake --build build
Hello from script, Ninja!
[ 0%] Built target my-script
...
If you need something more complex than an environment variable, you can introduce condition statement based on value of CMAKE_GENERATOR:
cmake_minimum_required(VERSION 3.20)
project(Hello)
add_executable(Hello main.cpp)
if(CMAKE_GENERATOR STREQUAL Ninja)
add_custom_target(my-script COMMAND ${CMAKE_CURRENT_SOURCE_DIR}/script.sh $ENV{SCRIPT_ARG})
elseif(CMAKE_GENERATOR STREQUAL "Unix Makefiles")
add_custom_target(my-script COMMAND ${CMAKE_CURRENT_SOURCE_DIR}/another_script.sh)
endif()
add_dependencies(Hello my-script)
The provided solutions work at build step, and for the part whether it's possible to distinguish between generators during build system generation phase (e.g. with use of generator expressions) i don't think it's possible, because the configuration is generator-agnostic at this point.