Enhancing CMake Builds with CMAKE_CPACK_COMMAND for Packaging Control

What is CMAKE_CPACK_COMMAND?

• It stores the full path to the cpack(1) executable installed with CMake.
• It's a CMake cache variable introduced in version 3.13.

Purpose

• These custom commands or tests can leverage the CMAKE_CPACK_COMMAND variable to invoke specific CPack functionalities programmatically during the build process.
• This variable is primarily intended for use within custom commands or tests defined in your CMakeLists.txt file.

Why is it Useful?

• Enables automation of packaging tasks or integration of CPack with custom build steps.
• Provides a way to interact with CPack functionalities from custom logic within your CMake project.

Example Usage

# Define a custom command to create a specific package format
add_custom_command(
    OUTPUT my_custom_package
    COMMAND ${CMAKE_CPACK_COMMAND}
            # Additional CPack arguments for creating the desired package
            INSTALL_MANIFEST DESTINATION share/doc/myproject
            PACKAGE_FILE_NAME myproject-custom.tar.gz
)

# Add the custom command as a dependency for a target
add_dependencies(my_installer my_custom_package)

Key Points

• This variable allows programmatic control over CPack actions within your CMake build scripts.
• Use additional CPack arguments within your custom command to define the packaging behavior.
• CMAKE_CPACK_COMMAND provides the path to the CPack executable, not the CPack configuration itself.

• Ensure CMake is configured to install CPack during installation for CMAKE_CPACK_COMMAND to be populated correctly.

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Creating a Custom Installer

This example creates a custom installer using the CPACK_GENERATOR argument:

add_custom_command(
    OUTPUT my_installer
    COMMAND ${CMAKE_CPACK_COMMAND}
            CPACK_GENERATOR NSIS
            # Additional arguments specific to NSIS installer generation
            INSTALL_RUNPATH "${CMAKE_INSTALL_PREFIX}/bin"
)

# Add the custom command as a dependency for your main target
add_dependencies(your_target_executable my_installer)

Generating Package Lists

This example generates a package list file using the CPACK_PACKAGE_FILE_NAME argument:

add_custom_command(
    OUTPUT package_list.txt
    COMMAND ${CMAKE_CPACK_COMMAND}
            GENERATE
            PACKAGE_FILE_NAME package_list.txt
)

# Use the generated package list for further processing (optional)
message(STATUS "Package list generated: ${package_list.txt}")

Configuring Specific Package Content

This example demonstrates excluding a directory from the package using the CPACK_SET_COMPONENT_PACKAGE_DATA argument:

# Define a component for your project files
add_component(myproject_files FILES main.cpp header.h)

# Exclude a specific directory from the "myproject_files" component
set(CMAKE_CPACK_COMPONENT_PACKAGE_DATA "myproject_files" EXCLUDE some_excluded_directory)

# Use CPack to create a package with the configured component
include(CPack)
cpack(PACKAGE_DESTINATION ${CMAKE_CURRENT_BINARY_DIR}/package)

Remember to replace placeholders like your_target_executable and some_excluded_directory with your specific project details.

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Using the cpack() Function

• This method is generally recommended for most scenarios as it's more convenient and streamlines CPack integration into your build process.
• You can specify packaging configuration directly within your CMakeLists.txt file using commands like CPACK_GENERATOR, PACKAGE_FILE_NAME, and others.
• The standard approach for interacting with CPack is through the built-in cpack() function. This function simplifies the process by providing a higher-level abstraction compared to directly invoking the cpack(1) executable.

# Use cpack() function for standard packaging configuration
include(CPack)
cpack(
    PACKAGE_DESTINATION ${CMAKE_CURRENT_BINARY_DIR}/package
    CPACK_GENERATOR DEB  # Or other packaging format like RPM, NSIS, etc.
)

Custom Scripting

• This approach offers greater flexibility but requires additional script maintenance and might be less portable compared to using built-in CMake features.
• These scripts could then be invoked during the build process using the execute_process() command in CMake.
• If your packaging requirements go beyond CPack's capabilities, you can create custom scripts for advanced packaging tasks. These scripts could be:
  • Bash/Shell scripts on Linux/macOS
  • Batch scripts on Windows
  • Python or other scripting languages for more complex logic

Choosing the Right Approach

The best approach depends on the complexity of your packaging needs:

• Advanced logic or non-CPack packaging
  Consider custom scripting with execute_process().
• Simple configuration
  Use the cpack() function for a streamlined experience.

• If you're new to CPack, it's recommended to start with the cpack() function and explore CMAKE_CPACK_COMMAND for more advanced use cases.
• CMAKE_CPACK_COMMAND can still be useful for specific scenarios where you need more granular control over CPack execution from within custom commands or tests.