py-posix-shell 0.4.0

A cross-platform POSIX-style shell written in Python.

py-posix-shell

py-posix-shell is a cross-platform POSIX-style shell implemented in pure Python. The long-term goal is to become a practical dash-like shell that can run on Windows, Linux, and macOS from the same Python package.

It is still young, but it now supports the pieces needed by many ordinary shell scripts:

• command lists with ;, &&, ||, background &, and !
• pipelines with |
• if/elif/else/fi
• for, while, and until loops with break and continue
• case/esac
• POSIX-style functions with return
• grouping with { ...; } and subshells with ( ... )
• quoting with single quotes, double quotes, and backslash escapes
• parameter expansion such as $HOME, $?, ${name:-word}, ${name:=word}, ${#name}, ${name#pattern}, ${name##pattern}, ${name%pattern}, and ${name%%pattern}
• arithmetic expansion with $(( expression ))
• command substitution with $(...) and backticks
• field splitting, pathname expansion, tilde expansion, and set -f
• here-documents with << and <<-
• redirection with <, >, >>, <>, 2>, 2>>, >&, and <&
• shell variables, exported environment variables, and positional parameters
• common builtins including ., :, alias, unalias, cd, pwd, eval, exec, exit, export, readonly, unset, set, shift, getopts, echo, printf, read, type, command, env, test, [, trap, umask, times, and hash
• internal POSIX/GNU-style utility fallbacks for hosts such as Windows where commands may be missing. The shell prefers a native command when it exists and otherwise falls back to Python implementations of common tools including ls, cat, cp, mv, rm, install, unlink, mkdir, rmdir, pwd, sort, uniq, wc, cut, head, tail, chmod, chown, chgrp, echo, date, sleep, printf, basename, dirname, whoami, yes, find, xargs, locate, updatedb, diff, cmp, diff3, sdiff, grep, egrep, fgrep, sed, awk, gawk, and tar

The implementation intentionally remains dependency-free at runtime. It aims for useful POSIX behavior first, then progressively tighter compatibility with dash.

Known gaps include job control, full signal semantics, complete interactive line editing, and exact set -e edge cases.

Installation

From PyPI:

pip install py-posix-shell

From this repository:

pip install .

For editable development:

pip install -e ".[dev]"

Usage

Start an interactive shell:

pysh

Run one command:

pysh -c "name=world; echo \"hello $name\""

Run a script:

pysh ./script.sh arg1 arg2

The package also installs the longer py-posix-shell command.

Development

Run the tests with:

pytest

Build the package with:

poetry build