zsh2xonsh

Have you heard of xonsh? It's a Python-powered shell.

You can do amazing things like this:

# Interpolate python -> shell
echo @(i for i in range(42))

# Interpolate shell -> python
for filename in `.*`:
    print(filename)
    du -sh @(filename)

# Execute regular shell commands too
cat /etc/passwd | grep root

As you can immagine, this awesomeness is not POSIX-compliant :(

This makes it difficult to setup your $PATH and do things like eval $(brew shellenv)

This package exists to translate traditional zsh scripts into xonsh code.

Compatibility (and how it works)

The goal is 100% compatibility for a subset of shell.

Compatibility is achived by delegating most of the work to zsh.

That is, export FOO="$(echo bar)" in a shell script becomes (essentially) $FOO=$(zsh -c 'echo bar') in xonsh.

We have zsh handle all the globbing/quoting/bizzare POSIX quirks.

In the face of ambiguity, or if we encounter an unsupported feature (like a for loop), then we fail-fast.

This is the most important feature. If something can't be supported 100%, then it will throw a descriptive error. Anything else is a bug :)

Features

The included shell features include:

1. Quoted expressions "$VAR glob/*" (zsh does expansion here)
2. Unquoted literals 12, foo ~/foo (mostly translated directly)
3. Command substitutions "$(cat file.txt | grep bar)"
   • zsh does all the work here
   • Supports both quoted and unquoted forms
4. If/then statements
   • Conditionals are executed by zsh (so [[ -d "foo" ]] works perfectly)
   • Translated into python if (so body will not run unless conditional passes)
5. Exporting variables export FOO=$BAR
   • Translates $PATH correctly (xonsh thinks it's a list, zsh thinks it's a string)
   • This is where the subprocess approach doesn't work blindly....
     • We support it cleanly by doing the left-hand assignment xonsh, and the right-hand expression in zsh :)
   • Local variables (local var=x) are supported too (with the proper scoping)
6. Support alias foo="bar"
   • This even supports globbing in the alias, so alias lsdot="echo .*" would glob in the same way that zsh does (experimental)
7. Basic support for function declarations (and having positional arguments)
   • Local variables are scoped properly inside the function :)
8. Support for 'echo' builtin as a python 'print'

You can also add "external builtins", which are extra commands that the script can invoke. In my own files, I use this to add an extend_path command (even though zsh2xonsh properly translates $PATH variables already, it's still a nice utility)

My macbook config is a good example of the full power of the translator. It supports function declarations, if/then statements and conditionals (all in an attempt to cleanup homebrew cludges lol).

All of these behaviors should be 100% compatible with their zsh equivalents. If you try anything else (or encounter an unsupported corner case), then you will get a descripitive error :)

Installation & Usage

This is a pypi package, install it with pip install zsh2xonsh.

The API is simple, run translate_to_xonsh(str) -> str to translate from zsh -> xonsh code. This does not require xonsh at runtime, and can be done ahead of time.

If you want to evaluate the code immediately after translating it (for example in a .xonshrc), you can use . This requires xonsh at runtime (obviously) and uses the evalx builtin.

Additionally you can use the CLI (python -m zsh2xonsh), which accepts an import.

If you want to provide extra utility functions to your code, you can define extra_builtins.

Example

In my .xonshrc, I dynamically translate and evaluate the output of brew shellenv:

zsh2xonsh.translate_to_xonsh_and_eval($(/opt/homebrew/bin/brew shellenv))

Likewise, I do the same with my machine-specific .config.zsh files (in the example directory).

Motiviation

First of all, I need support for eval $(brew shellenv) .

Second of all, I still use zsh as my backup shell (by the use of my wrap-shell utility).

This means I need to setup $PATH and other enviornment variables for both of these shells, indepenently of each other.

The natural way to set these up is by using shell scripts. I have a seperate one for each of my different machines (server, macbook, old lapotop, etc)

For each of these (tiny) shell scripts, zsh2xonsh works very well :)

So in addition to properly translating $(brew shellenv), it also needs to translate these basic shell "environement files".

Turns out, dealing with platform specific quirks can get pretty intense and requires things like function definitions and if/then statements. In order to properly support exports, control flow has to be emulated in Python (can't just delegate to zsh).