1   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.

2   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

3   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.