Emix

Emix lets a modern Unix machine pretend to be an older computer.

It is not a CPU emulator and it does not run historical binaries. It presents the commands, syntax, output formats and error messages of historical systems while operating on ordinary host files with ordinary host programs underneath. Your files stay real files.

Three personalities ship today:

They are not three programs. They are three vocabularies over one engine, and the differences between them — CP/M's NEW=OLD argument order, DCL's abbreviations and /QUALIFIERS, CMS's three-token FILENAME FILETYPE FILEMODE — are what the engine exists to express.

Install

Not yet released. Nothing has been published to PyPI yet, so the commands below that name emix-shell will not resolve until 0.2.0 ships. Run from a checkout meanwhile.

The distribution is called emix-shell; the command it installs is emix. PyPI rejects the bare name emix as too similar to the existing emux, emx and emi projects.

Emix has no runtime dependencies beyond Python 3.10 or newer.

Run from a checkout, with no install at all:

git clone https://github.com/rdubar/emix && cd emix
./emix cpm

Install it as a command, from a checkout:

uv tool install .        # or: pipx install .
emix cpm

Install on another machine — build a wheel and copy it across. The wheel is pure Python, so one build serves x86-64 and Apple silicon and Raspberry Pi alike:

uv build
scp dist/emix-*.whl pi:/tmp/
ssh pi 'uv tool install /tmp/emix-*.whl'

Once released, and once the repository is public, these will work:

uv tool install emix-shell                           # from PyPI
uv tool install git+https://github.com/rdubar/emix   # from source
uvx --from emix-shell emix cpm                       # without installing

Note the --from in the uvx line: the distribution is emix-shell but the command is emix, so uvx needs telling which package provides it.

If uv warns that ~/.local/bin is not on your PATH, run uv tool update-shell and open a new terminal.

Use

The current directory becomes the first drive. Mount more with --mount, which is repeatable; drives are named in each personality's own style, so the first mount is A: under CP/M, DKA0: under VMS and filemode A under CMS.

emix cpm                                  # . becomes A:
emix cpm --mount ~/Documents --mount ~/src  # A: and B:
emix vms --mount ~/Documents              # DKA0:
emix cms --mount ~/Documents              # filemode A
emix cpm -c "DIR *.TXT"                   # run one command and exit

A CP/M session:

EMIX 0.2.0
CP/M 2.2 PERSONALITY
A: /Users/rdubar/dev/emix
TYPE HELP FOR AVAILABLE COMMANDS.

A>DIR *.MD
A: README   MD  A: ROADMAP  MD

A>PIP NOTES.TXT=README.MD
A>STAT
A: R/W, SPACE: 96,508,384K
A>python3 hello.py
Hello from Unix
A>EXIT
RETURNING TO UNIX.

The same drive under DCL:

$ DIRECTORY/SIZE

Directory DKA0:[000000]

README.MD;1                     6
ROADMAP.MD;1                    9

Total of 2 files, 15 blocks.

$ DELETE README.MD
%DELETE-W-NOVER, explicit version number required

and under CMS, where a file is three words and the system answers Ready;:

LISTFILE
README   MD       A1
ROADMAP  MD       A1
Ready; T=0.01/0.01 21:42:19

What is authentic and what is not

Emix aims to be recognisable, and says so when it is not.

Authentic. CP/M's six CCP built-ins are exactly the six it had; PIP and STAT are listed separately because they were transient .COM programs loaded from disk, not built-ins. REN NEW=OLD and PIP DEST=SOURCE keep their surprising destination-first order. DCL verbs abbreviate to any unambiguous prefix. DELETE demands an explicit version, as VMS did. CMS answers Ready; T=... after every command and Ready(00028); after a failure. Error messages follow each system's house format — NO FILE, %RMS-E-FNF, file not found, DMSxxx002E File 'X' not found.

Deliberately not authentic. ERA confirms every erase, where CP/M only confirmed for ERA *.*, because these are your real files. Names that do not fit 8.3 are shown in full rather than truncated, because a listing that names a file you cannot then type is worse than a misaligned column. HELP, CLS, VER, UNIX and DRIVES are Emix conveniences and are labelled as such in HELP. File versions display as ;1 but only one copy is stored.

Not yet built. CP/M user areas, reversible 8.3 aliases, VMS directory syntax and real file versions, CMS EXEC and XEDIT. See ROADMAP.md.

Safety

Emix runs on your real home directory, so the boundaries are explicit and tested:

• Drives are sealed. Every path is resolved through the host layer and checked against its drive root after symlinks are followed, so a symlink pointing out of a drive is neither readable nor listed. Directory traversal, absolute paths and separators in file names are rejected.
• No shell is ever invoked. Unknown CP/M commands are offered to the host as executables via subprocess with an argument list. Because there is no shell, |, >, &&, $VAR and backticks are literal arguments rather than operators. Exit Emix when you want a real shell. VMS and CMS do not fall through at all; use RUN/SPAWN and CMS.
• Case ambiguity fails loudly. On a case-sensitive host holding both readme.txt and README.TXT, Emix reports the ambiguity rather than silently picking whichever the filesystem happened to list first.
• Destructive commands confirm, and anything but an explicit Y/YES means no.

Erasing a file in Emix erases it on the host. That is the point of the project, and the reason for everything above.

Development

uv sync           # create the environment
uv run pytest     # 62 tests
uv run ruff check . && uv run ruff format --check .
uv run mypy       # strict

Layout:

src/emix/
  errors.py         symbolic error codes, worded by each personality
  host.py           drives: containment, case folding, ambiguity
  shell.py          the REPL, verb table, abbreviation, host fallthrough
  cli.py            argument parsing and drive mounting
  personalities/    cpm.py, vms.py, cms.py — vocabulary and house style

Adding a personality means one module and one line in personalities/__init__.py. Verbs are methods marked with @verb; the base class handles parsing, dispatch, confirmation, history and errors.

Status

Emix is an early experiment, version 0.2, not yet released. It is useful for real file browsing today, and is tested on macOS and on a Raspberry Pi 5 — the case-sensitive filesystem there is the interesting case. The roadmap covers where it goes next, including the question of whether it should eventually execute genuine CP/M .COM binaries in a sandbox — and why the answer turns out to be less frightening than it sounds.

MIT licensed.