ShellCreator 0.2

A library to create command line interfaces.

Shell Creator

This is a simple python library that can be used to create entire shells for CLI applications. It was originally a part of another application, and then I decided to split it and make it a library on its own. The shell has following features:

• Python like arithmetic operators
• Setting/Unsetting variables
• Builtin commands for variable manipulation
• Builtin support for if statements and while loops (not yet implemented)
• Easily extensible with new commands through simple class inheritance
• Colorful, with nice logging

How to use

Help and Exiting

use the following commands to get help and exit:

• help --commands will give you the list of all commands in the shell
• help --variables will give you the list of all variables in the shell
• exit to exit the shell

Operators

The shell uses the same python arithmetic operators for convenience, it also maintains their precedence and associativity. The operators are:

Operator	Description
**	Exponent
-x	Unary minus
*, /, //, %	Multiplication, Division, Floor division, Modulus
+, -	Addition, Subtraction
==, !=, >, >=, <, <=	Comparisons
not	Logical NOT
and	Logical AND
or	Logical OR

WARNING: Chaining comparison arguments will have a different effect from python. The shell will parse them one by one, in other words: a < b > c will be parsed as (a < b) > c rather than a < b and b > c

Variables

The shell can handle saving, deleting, and accessing variables in the following ways:

echo $var
set var=$var2 + 485 * 12
unset $var

When dealing with variables pay attention to the following points:

• Reading a shell variable must precede its name with a $.
• Writing to a variable must NOT precede its name with a $.
• Setting an existing variable will overwrite its existing value.
• Unsetting or Echoing a non-existent variable will generate an error.

If and While

TODO

Adding commands

The Shell Creator utilizes the great docopt library to build the commands of the shell (including the builtin ones). There's a base Command class that must be inherited and overridden to implement new commands. Example:

class ReadFile(Command):
  usage='''
  read_file

  Usage:
      read_file -h
      read_file [--f FORMAT] FILE

  Options:
      -h, --help                    Print this help message
      -f FORMAT, --format=FORMAT    The format of the file to read
  '''

  @classmethod
  def action(cls):
      print(cls.args)
      print(cls.args['FORMAT'])
      print(cls.args['FILE'])

  addCommand('read_file', ReadFile)

Styling

The shell uses logging for logging, with the namespace SHELL. It utilizes this formatter to better format and colorize logging. It also uses prompt_toolkit's styling to style the prompt itself. You can refer to the examples or to prompt_toolkit's documentation for more details

Prerequisites and Installation

TODO