Do you know Lua? Not quite Perl, but usable, and written entirely in C. Small enough to run on an 8 bit AVR microcontroller. So it should be possible to run on a C64 or similar.
- Forth, used for Open Firmware (a.k.a. OpenBoot) in Sun, Apple, IBM, various ARM systems
- MUMPS, originally designed to run on 1960s hardware. It is a very compact, yet very powerful combination of language interpreter, database, and multi-user, multi-tasking operating system. Learning all of MUMPS takes no more that 10 days if you know Perl, expect to write your first non-hello-world program end the end of day 1. Some of my postings contain example MUMPS code.
Today I will gladly share my knowledge and experience, for there are no sweeter words than "I told you so". ;-)