Shnake:

Python3 library to make command-line tools

Introduction

Shnake is a generic command interpreter with multicommand support.

The shnake library has been initially developped to correctly handle the phpsploit framework shell interfaces. Therefore, it was built in order to stand generic, and usable by any other open-source project.

• The shell part extends the pretty good cmd standard library, adding many new features, and a few new behaviors.
• The shnake lexer depends on the pyparsing library.

It was built to theorically work on all 3.x python versions. For any bug, issue or enhancement proposal, please contact the author.

NOTE:

• The shnake library extends and wraps the cmd python standard library. So a little knowledge of cmd it required to ease shnake comprehension.

Requirements

Mandatory dependencies:

pyparsing

Optional dependencies:

readline

Tested with python3.4

Features

Command line interface

• The command line interpreter has been highly enhanced, with a complete overwrite of the parseline() method, to provide the most bash-like features as possible.
• Multi commands, separated by semicolons can now be typed.
• Multi line command also can be written, like on bash prompt by ending a line with a backslash, prompting the user to continue writing the command in the next line (like bash's PS2).
• Strings can now be enquoted, to be processed as a single argument.

Command execution

• An argv array of arguments is now passed as do_foo() argument (an all other cmd related methods) instead of the cmd tuple.
• The interpret() method can be used to eval a string as a list of shnake commands. It also can be used inside do_* commands.

Prompt feature

• Included an input() wrapper (classe's raw_input() method) that makes use of regular expressions to automatically enclose enventual prompt's ANSI color codes with \x01%s\x02, fixing readline's prompt length missinterpretation on colored ones.
• Since multiline commands are supported, a new variable: prompt_ps2 can be used to change PS2 prompt prefix.
• EOFError raised during input() are the same as sending the exit command to the interpreter.

Exception handling

• The new onexception() method has been made to handle exceptions. It eases a lot command methods (do_foo()) development, allowing them to simply raise exceptions on error, that will be automatically handled and represented by a standard error line.
• An exception foo is dispatched to a method except_foo if available; the except_ method is passed a single argument, the exception object itself.
• The new variable error defines the error line template.

Command return values

• Adding support for command return values. Instead of the cmd trivial boolean behavior, any command are now able to return anything. The postcmd method manages integer return values, in a similar way than the sys.exit's behavior.
• To leave the cmdloop() method, a SystemExit must be raised (with the exit() built_in function for example)

Misc behaviors

• Extended the get_names() method, which now can take an instance as argument, limiting the returned attributes to this one.
• Unlike cmd lib, emptyline()'s default behavior defaultly does nothing instead of repeating the last typed command (bash like).
• Typing EOF to leave is not used on shnake, consider using exit and raise SystemExit instead.
• The classe's default() method had been enhanced, writing command representation in case of unprintable chars, and also takes use of the new nocmd variable.
• When left, the cmdloop() methods acts exactly in the same way that command return values behavior, meaning that the return value will be an interger anyway, 0 in case of no error.

Limitations & Other changes

• Unlike cmd , the shnake library do not provides support for command line interpretation without input() built-in function.
• Unlike cmd, shnake is NOT compatible with python 2.x.