CS60 Homework Assignment 9
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Due: Oct 29th at 1:00pm


Pipe!
---------------------

The task of homework 9 is to create a program that takes two commands
as arguments, creates a pipe, redirects the standard out from the
first process to the standard in of the second, and executes the
processes.  This is exactly what happens when a shell is given a
command of the form:

cmd1 | cmd2

And if completed, should aid in the completion of project3's extra
credit opportunity.

You program should perform simple error checking for the following
cases:

1.) user has not specified two commands to execute
2.) commands cannot be executed by execv()

Hints
-----------------

Read the book and look at the manpages for fork(), dup2(), and
execvp().

Turnin
------------------

The turnin tag for this assignment is 'hw9' and must include the code,
a scriptfile showing compilation and execution of the program with at
least the 'ls' and 'wc' commands as arguments to your program, as well
as the 'ls | wc' command at a shell prompt.  For compilation, you must
show your program compiling with the '-ansi -pedantic' flags to
gcc. You may include an optional README file with special instructions
for the grader.

Sample Output
------------------

[nurmi@localhost hw9]$ gcc hw9.c -o hw9
[nurmi@localhost hw9]$ ./hw9
USAGE: ./hw9 <cmd1> <cmd2>
[nurmi@localhost hw9]$ ./hw9 ls
USAGE: ./hw9 <cmd1> <cmd2>
[nurmi@localhost hw9]$ ./hw9 ls wc
       9       9      71 
[nurmi@localhost hw9]$ ls | wc
       9       9      71 
[nurmi@localhost hw9]$