Hi I have an old version of boost 1.33.1. I want to build it with a custom gcc binary whih is in a path other than default. I could not find the page on the web so I paste the first part of the gcc-tools.jam form tools/build/v1/gcc-tools.jam. # singleton variables... set-as-singleton GCC_ROOT_DIRECTORY GCC_BIN_DIRECTORY GCC_INCLUDE_DIRECTORY GCC_STDLIB_DIRECTORY ; flags gcc GCC_BIN_DIRECTORY : $(GCC_BIN_DIRECTORY) ; flags gcc GCC_INCLUDE_DIRECTORY : $(GCC_INCLUDE_DIRECTORY) ; flags gcc GCC_STDLIB_DIRECTORY : $(GCC_STDLIB_DIRECTORY) ; GCC_BIN_DIRECTORY ?= $(GCC_ROOT_DIRECTORY)$(SLASH)bin ; GCC_BIN_DIRECTORY ?= "" ; # Don't clobber tool names if GCC_ROOT_DIRECTORY not set GCC_STDLIB_DIRECTORY ?= $(GCC_ROOT_DIRECTORY)$(SLASH)lib ; # Make sure this gets set "on" the target flags gcc GCC_BIN_DIR : $(GCC_BIN_DIRECTORY) ; In this part I can modify the default gcc/g++ to my own using the variables which are defined in the comment section. However I don't know How to do that. For example, I write GCC_BIN_DIRECTORY=/opt/gcc-4.1.2/installed But that gives me this error: rule GCC_ROOT_DIRECTORY=/opt/gcc-4.1.2/installed unknown in module So how can I do that? Regards, Mahmood