===========
 MiniShell
===========

Deadline: October 31st, 2014. **For this assignment you may work in pairs.**

.. sectnum::

Instructions
============

You must implement a program ``minish`` which can be used as a Unix
shell.

``minish`` must support at least simple commands with zero or more
arguments, and commands separated by semicolons. Extra whitespace must
be condensed. For example ``echo hello ; echo world`` must behave the
same as ``echo hello;echo world``. The shell must also support the
built-in commands ``exit`` and ``cd``; both with either zero or one
argument.

You must then choose a selection of features in the following set
to achieve a passing grade and beyond, see Grading_ below:

- Command pipelines, eg. ``ls | grep foo``
- Simple redirections at the end of simple commands, eg. ``tr a-z A-Z
  <fin >fout``
- File globbing: support for expanding ``*``, ``?`` etc. in a command
  line into a list of files/directories using ``glob(3)``.
- Setting or unsetting environment variables with ``setenv`` and
  ``unsetenv``.  (Note: you need not implement variable expansion. If
  you do, it must be unsurprising.)
- Simple quoting: ``"foo bar"`` is passed as a single argument.  Must
  support simple ``\`` escapes: ``"foo\"bar"`` counts as one argument
  with 7 characters (``foo"bar``). If globbing is supported, quoting
  must disable globbing, ie. ``"*"`` is not expanded and passed
  as a single character.
- Command groups enclosed in ``{...}`` (same shell) or ``(...)`` (sub-shell).
- Job control: ``command &`` detaches; Ctrl+Z suspends, ``jobs`` lists
  the currently managed jobs; ``fg``/``bg`` resumes a job in the
  foreground or background.
- Any extra feature you deem particularly useful.

Constraints:

- You must only depend on standard C functions (either from ISO C 1999/2011 or
  POSIX).
- You must not use ``system`` or any other mechanism that invokes an
  existing shell to execute the command lines.


Example commands
================

::

   $ echo hello; touch /tmp/hello.txt
   hello
   $ ls /tmp | grep .txt
   hello.txt
   $ ls /dev >/tmp/hello.txt
   $ tr d @ </tmp/hello.txt | grep st@
   st@err
   st@in
   st@out

   # Example globbing:
   $ ls /dev/std* /tmp/*.c

   # Example quoting:
   $ echo "hello;\n world"
   hello;n world

   # Example environment variables:
   $ setenv MY hello
   $ bash -c "echo $MY"
   hello

   # Example command groups:
   $ ( echo hello; echo world ) >hello.txt
   $ tr \n . <hello.txt
   hello.world

   $ setenv I hello; { setenv I world }; bash -c "echo $I"
   world
   $ setenv I hello; ( setenv I world ); bash -c "echo $I"
   hello


Grading
=======

- 3 points if your shell properly handles simple commands separated by
  semicolons, and if the built-ins ``exit`` and ``cd`` are properly
  implemented.
- +2 points if command pipelines are properly supported.
- +1 point if simple redirections are properly supported.
- +1 point if ``setenv/unsetenv`` are properly supported.
- +1 point if simple quoting is properly supported.
- +2 points if file globbing is properly supported.
- +2 points if command groups are properly supported.
- +4 points if job control is properly implemented.
- +2 point if any additional feature is implemented and
  duly documented in an enclosed ``README`` file, and
  your examinator agrees it is indeed useful.

Tips: the maximum grade is 10; there are multiple ways to get
there. As usual, go for correctness before completeness. Test a
lot. Use version control. Consider pair programming.

----

Copyright and licensing
=======================

Copyright © 2014, Raphael ‘kena’ Poss.  Permission is granted to
distribute, reuse and modify this document and other documents for the
Systems Programming course by the same author according to the terms
of the Creative Commons Attribution-ShareAlike 4.0 International
License.  To view a copy of this license, visit
`http://creativecommons.org/licenses/by-sa/4.0/
<http://creativecommons.org/licenses/by-sa/4.0/>`_.