Is there some Linux based macro system for generating G codes. Say, I
wanted to mill out a rectangular pocket, or drill a bolt hole pattern
etc. I would love to use a preprocessor like macro systems for
assemblers, or C preprocessor type thing that would be eared towards
CNC machining.

I can probably do something homegrown, but would prefer to find
something that is well thought out.

Writing text files with commands does fit my personality, but I woud
prefer to be able to create my own higher level commands.

i