Simple Shell Parser

A simple shell parser in pure Python that interprets shell pipelined commands and redirections such as the following:

foo toto > bar 2>> baz | fizz >> fuzzz << EOF | goo > gooo < gaa 2> ga | dummy

This parser is meant for educational purpose and, therefore, should not be relied on for advanced projects. It is built using the very nice parglare python parser.

The parsing of a command like the previous one produces a simple Abstract Syntax Tree: a collection of objects that reflect the syntax structure of the line being parsed.

At the root level, we find the object associated to the whole line, the pipeline. It is a simple python List. The list elements are intances of the PROCESS class defined in the parser module. Each process owns attributes for the arguments and redirections. They can also be displayed using an explicit string representation as follows:

#!/usr/bin/env python3
import lexer as ssp

result = ssp.get_parser().parse('foo toto > bar 2>> baz | fizz >> fuzzz << EOF | goo > gooo < gaa 2> ga | dummy')

for p in result: print(p)

which produces the following output:

$ python example.py
Proc(cmd=foo [toto], redirs=[OUTREDIR(bar), ERRREDIR(baz,append=True)])
Proc(cmd=fizz [], redirs=[INREDIR(EOF,here=True), OUTREDIR(fuzzz,append=True)])
Proc(cmd=goo [], redirs=[INREDIR(gaa), OUTREDIR(gooo), ERRREDIR(ga)])
Proc(cmd=dummy [], redirs=[])
$

All elements displayed in the previous output are objects of the following classes:

• PROCESS
• CMD
• REDIR (INREDIR, OUTREDIR, ERREDIR)

The pipeline is list of PROCESS objects and the command args are also a list object attribute of the CMD class.

See the lexer.py source code or the python doc for more details ...

PREREQUISITE

This python module requires python version 3.X. In case this version is not already installed and you do NOT have admin permissions, you can still install the latest version of python using pyenv. For example as follows with shell zsh (see also instructions on pyenv page for other environments):

$ git clone https://github.com/pyenv/pyenv.git ~/.pyenv
$ echo 'export PYENV_ROOT="$HOME/.pyenv"' >> ~/.zshrc
$ echo 'export PATH="$PYENV_ROOT/bin:$PATH"' >> ~/.zshrc
$ echo 'if command -v pyenv 1>/dev/null 2>&1; then\n  eval "$(pyenv init -)"\nfi' >> ~/.zshrc
$ source ~/.zshrc
$

Then install the desired python version, eg. 3.6.4:

$ pyenv install 3.6.4
$

And finally make this version your new default version and re-read your shell environement file:

$ pyenv global 3.6.4
$ source ~/.zshrc
$

If no error occured so far, your set to go!

INSTALL

This python module is available through PyPi using the following command:

$ pip install simple-shell-parser
$