Cmake can write files and fill in/expand variables. For pkg-config
configure_file(pkg-config.pc.in my_package.pc @ONLY)
expands
# pkg-config.pc.in
prefix="@CMAKE_INSTALL_PREFIX@"
exec_prefix="${prefix}"
libdir="${prefix}/lib"
includedir="${prefix}/include"
Name: @PROJECT_NAME@
Description: @CMAKE_PROJECT_DESCRIPTION@
URL: @CMAKE_PROJECT_HOMEPAGE_URL@
Version: @PROJECT_VERSION@
Requires: @pc_req_public@
Requires.private: @pc_req_private@
Cflags: -I"${includedir}"
Libs: -L"${libdir}" -l@target1@ -l@target2@
Libs.private: -L"${libdir}" -l@target1@ -l@target2@ @pc_libs_private@