CMake: How to Fetch a Single File From the Git Repository

To fetch a single file from a Git repository using CMake, you can't do it directly with CMake alone, as CMake doesn't have built-in support for partial file retrieval from a Git repository. However, you can use execute_process in CMake to run Git commands that fetch only the file you need.

A Step-by-step Guide

• Set up Variables: Define the URL and the target file path.
• Run Git Archive to Retrieve a Single File: Use git archive to create an archive of just the specified file and then extract it.
• Integrate with CMake: Use CMake’s execute_process command to run these Git commands.

# Define variables
set(GIT_REPO "https://github.com/user/repo.git")
set(FILE_PATH "path/to/your/file.txt")  # Relative path within the repo
set(DEST_DIR "${CMAKE_BINARY_DIR}/downloaded_file")

# Create the directory if it doesn’t exist
file(MAKE_DIRECTORY ${DEST_DIR})

# Use git archive to get only the specified file
execute_process(
	COMMAND git archive --remote=${GIT_REPO} HEAD ${FILE_PATH} | tar -x -C ${DEST_DIR}
	RESULT_VARIABLE result
)

# Check if the file was successfully downloaded
if(result)
	message(FATAL_ERROR "Failed to download file ${FILE_PATH} from ${GIT_REPO}")
else()
	message(STATUS "Successfully downloaded ${FILE_PATH} to ${DEST_DIR}")
endif()

Conclusion

By using git archive with execute_process in CMake, you can fetch a single file from a Git repository without the overhead of cloning the entire repository. This method is straightforward, efficient, and integrates well with existing CMake workflows, ensuring you only retrieve the files you need for your project.