Advanced Operating Systems P2

                        Advanced Operating Systems
                               


Enhance the shell from p1 to support the new facilities described below.


-------- Commands Other Than Builtin --------
In addition to builtin commands, permit the user to execute commands
that are executable programs which can be located via AOSPATH.  If
there are multiple commands by the same name use the first one in the
path.  If a program happens to have the same name as a builtin command,
use the builtin one.  Note the user can skip use of the path and builtin
by providing a relative or full pathname.

Execution of programs should be done in a separate process created via
fork.  The exec system call should also be used in the separate process
to run the specified program.

By default, the shell should wait for an executed program to run.
However, if the user places an & at the end of the command, then the shell
should create the separate process to execute as background, and then
produce a new prompt for the user to do other things.  The shell should
print a useful message to the user when a background process terminates.


-------- I/O Redirection --------
The user should also be able to run processes in this manner:
    p1 | p2   ## which would cause stdout of p1 to go to p2's stdin
You can use pipe and dup/dup2 to assist in such an operation.

We are NOT supporting < or > type operations at this time.


-------- Process Limits --------
Provide a new builtin command name "lim" which affects any processes 
created thereafter.  lim takes either no args, or exactly 2 args.

    lim  ## no args; prints the current limits being used
    lim cputime memory  ## setrlimit CPU or AS
        lim 3 4  ## (max of 3 seconds cputime and 4 MB of memory)


Submitting the project for grading:

The project should compile and link as p2.

You should turnin a tar file containing all of the required files.

To build the project, I will cd to my directory containing your files
and simply type:

    rm -rf p2
    rm -rf *.o
    make