Python Pluggable Shell Interface
Project description
Develop extensible and powerful command line interface shells with minimal code. Want to jump straight into the API? Take a look at Pypsi Shell and Command Tutorial.
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.
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.
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.
Features
The following capabilities ship with pypsi and are available out of the box.
I/O redirection
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. The demo.py file is meant to be a reference to the Pypsi API and design. Use it as a starting point for your first shell.
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
Prompt Wizards
Prompt wizards ask the user a series of questions and request input. Input is tab completed, validated, and returned. The wizard can be used for easy configuration of components that require a substantial amount of input.
pypsi)> wizard +-----------------------------------------------------------------------------+ | Entering Example Configuration Wizard | +-----------------------------------------------------------------------------+ Shows various examples of wizard steps To exit, enter either Ctrl+C, Ctrl+D, or 'quit'. For help about the current step, enter 'help' or '?'. IP Address: <enter> Error: Value is required Local IP Address or Host name IP Address: 192.168.0.10 TCP Port [1337]: <enter> File path: /var/lo<tab> local/ lock/ log/ File path: /var/log/<tab> Xorg.1.log btmp faillog upstart/ Xorg.1.log.old dist-upgrade/ fontconfig.log wtmp alternatives.log distccd.log fsck/ apt/ dmesg lastlog bootstrap.log dpkg.log mongodb/ File path: /var/log/dpkg.log Shell mode [local]: asdf Error: Invalid choice Mode of the shell Shell mode [local]: remote Config ID Config Value ================================================================================ ip_addr 172.16.11.204 port 1337 path /var/log/dpkg.log mode remote
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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