# CPACK_CUSTOM_INSTALL_VARIABLES

New in version 3.21.

CPack variables (set via e.g. `cpack -D`, `CPackConfig.cmake` or `CPACK_PROJECT_CONFIG_FILE` scripts) are not directly visible in installation scripts. Instead, one can pass a list of `varName=value` pairs in the `CPACK_CUSTOM_INSTALL_VARIABLES` variable. At install time, each list item will result in a variable of the specified name (`varName`) being set to the given `value`. The `=` can be omitted for an empty `value`.

`CPACK_CUSTOM_INSTALL_VARIABLES` allows the packaging installation to be influenced by the user or driving script at CPack runtime without having to regenerate the install scripts.

## Example

    install(FILES large.txt DESTINATION data)

    install(CODE [[
      if(ENABLE_COMPRESSION)
        # "run-compressor" is a fictional tool that produces
        # large.txt.xz from large.txt and then removes the input file
        execute_process(COMMAND run-compressor $ENV{DESTDIR}${CMAKE_INSTALL_PREFIX}/large.txt)
      endif()
    ]])

With the above example snippet, `cpack` will by default run the installation script with `ENABLE_COMPRESSION` unset, resulting in a package containing the uncompressed `large.txt`. This can be overridden when invoking `cpack` like so:

    cpack -D "CPACK_CUSTOM_INSTALL_VARIABLES=ENABLE_COMPRESSION=TRUE"

The installation script will then run with `ENABLE_COMPRESSION` set to `TRUE`, resulting in a package containing the compressed `large.txt.xz` instead.