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Python Pluggable Shell Interface

Project description

Python Pluggable Shell Interface, or pypsi, is a framework for developing command line based shell interfaces, akin to bash or csh. It is intended to be a replacement for the builtin Python cmd module. A cmd plugin is available for use to make the transition from cmd-based shells to Pypsi.

Pypsi is targetted towards both rapid prototype interfaces and large stable shells. The bootstraping code is very small with very little boilerplate. Pypsi ships with a great deal of capabilities out of the box, all of which can be used or ignored. Pypsi is pluggable which allows commands, features, and plugins to be developed independently in their own source files and/or Python classes. This results in a very clean source repository. The actual code to setup and run the shell is exetremely small, on the order of ~20-50 lines of code.

Pypsi, at its core, is pluggable. There are many hooks that allow plugin authors to extend and modify the core behavior of pypsi. Commands are isolated classes that make distribution, sharing, and modification easy.

Caveats

The only major caveat when using pypsi is that it only supports Python 3. Python 3 is the future.

Releases

The pypsi source code is hosted at GitHub and releases are stored at PyPI. The latest version can also be install via pip:

pip install pypsi

Documentation can be found on GitHub Pages, Python Hosted, and on Read the Docs.

Features

The following capabilities ship with pypsi and are available out of the box.

  • I/O redirection
  • String-based pipes
  • Flexible API
  • Tab completion
  • Multiplatform
  • Minimal dependencies
  • Colors
  • Session tips and message of the day (MOTD)
  • Automated help, usage messages, and argument parsing
  • Word wrapping
  • Term highlighting (grep)
  • Tables
  • Prompt wizards
  • cmd plugin to migrate existing cmd commands into pypsi

Demo

The demo.py source file can be run to show off some of the base commands and features that ship with pypsi (the demo.py file can be downloaded from the git repo at https://github.com/ameily/pypsi/blob/master/demo.py). The commands displayed below are all optional: pypsi does not require the use of any command or plugin.

Variables

pypsi)> var name = "Paul"
pypsi)> var house = "Atredis"
pypsi)> echo My name is $name, and I belong to House $house
My name is Paul, and I belong to House Atredis
pypsi)> var -l
name     Paul
house    Atredis
pypsi)> var -d name
pypsi)> echo $name

pypsi)> var name = "Paul $house"
pypsi)> echo $name
Paul Atredis

I/O redirection

pypsi)> echo Hello
Hello
pypsi)> echo Hello > output.txt
pypsi)> echo Goodbye
pypsi)> xargs -I{} "echo line: {}" < output.txt
line: Hello
line: Goodbye
pypsi)> cat output.txt | grep ll
Hello

System commands

Allows execution of external applications. Command mimics Python’s os.system() function.

pypsi)> ls
pypsi: ls: command not found
pypsi)> system ls
include/
src/
README.md
pypsi)> system ls | system grep md
README.md

Fallback command

Allows the developer to set which command gets called if one does not exist in the current shell. This is very useful, for example, if you want to fallback on any OS installed executables. In this example, the fallback command is system.

pypsi)> ls
include/
src/
README.md

Command chaining

pypsi)> echo Hello && echo --bad-arg && echo goodbye
Hello
echo: unrecgonized arguments: --bad-arg
pypsi)> echo Hello ; echo --bad-arg ; echo goodbye
Hello
echo: unrecgonized arguments: --bad-arg
goodbye
pypsi)> echo --bad-arg || echo first failed
echo: unrecgonized arguments: --bad-arg
first failed

Multiline commands

pypsi)> echo Hello, \
> Dave
Hello, Dave
pypsi)> echo This \
> is \
> pypsi \
> and it rocks
This is pypsi and it rocks

Macros

Macros are analogous to functions in bash. They provide the ability to create new commands in the shell.

pypsi)> macro hello
> echo Hello, $1
> echo Goodbye from macro $0
> end
pypsi)> hello Adam
Hello, Adam
Goodbye from macro hello

Background

I developed Pypsi while working on a commerical product with a command line interface. Originally, we used the cmd module, which was fine when we only had a few commands that didn’t accept complex arguments. As we added more commands and more features, maintainability and extensibility became extremely complicated and time consuming.

I took what I had learned from the cmd module, ORM libraries such as MongoEngine, and features from proven great command line interfaces such as Git and then I developed Pypsi. In order for Pypsi to be viable for our project, I knew that Pypsi had to be compatible with cmd, the porting process had to take as little time as possible, and it had to be easy to understand and maintain.

The porting process from cmd to Pypsi for our commerical project took place in January 2014. Since then, we’ve had 4 stable releases, had real world feedback, and have successfully created many Pypsi commands and plugins with ease.

License

pypsi is released under the BSD 3-Clause license.

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