How do I use a shellscript for compilation?

[cronholio]

I need to use some custom (bash) shell scripts to compile code that has only recently been converted to a C::B project. In fact, I don't want C::B to invoke any compiler for me, but just run a specified script depending on the build target. I already gave it a shot and tried to run Squirrel's system command from within a build script but it didn't work. Any ideas?