Organization

• Directories that contain CMakeLists.txt are the entry point for the build system generator. Subdirectories can be added with the add_subdirectory() and must contain a CMakeLists.txt too.
• Scripts are <script>.cmake files that can be executed with the cmake -P <script>.cmake. Not all commands are supported.
• Modules are <script>.cmake files located in the CMAKE_MODULE_PATH. MOdules can be loaded with the include() command.

Commands

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command_name(space seperated list of strings)

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• Scripting commands change the state of command processor
  • set variables
  • change behavior of other commands
    
    
• Project commands
  • create build targets
  • modify build targets
    
    
• Command invocations are not expressions.

Variables

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set(myvar world)

message(STATUS "hello ${myvar})

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• Set withe the set() command.
• Expand with ${}.
• Variables and values are strings.
• Lists are ; seperated strings.
• CMake variables are not environment variables (unlike Makefile).
  
• Unset variable expands to empty string.

Comments

Use # for single line comments.

Custom Functions/Macros

• Commands can be added with function() or macro().
• When a new command replaces an existing command, the old one can be accessed with a _ prefix.
  
  

• Variables are scoped to the function unless set with the PARENT_SCOPE. 
• Available variables: input, output, ARGC, ARGN, ARG0, ARG1, ...
• Example: ${output} expands to bar.

• No extra scope with macros.
• Text replacements: ${input}, ${output}, ${ARGC}, ${ARGV}, ${ARGN}, ${ARG0}, ...
• Example: ${output} is replace by bar.

CREATE macros to wrap commands that have output parameters. Otherwise, create functions.

References

https://www.youtube.com/watch?v=bsXLMQ6WgIk