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 :)

All of these behaviors are 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))

Motiviation

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

Second of all, I still use zsh as my backup shell.

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

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 basic shell "environement files".