You will be writing a program that uses the system command line
arguments to produce useful outputs. The majority of the code in this
project should be dedicated to parsing command line in a robust way
and then feeding those to a useful program. Some time will be spent
configuring the system call string for ls and awk. You should use a
Makefile to compile your code and be sure there are no errors by using
-Wall and -Werror.


The executable for this project will be called "lopt"

This command will execute the ls function call using awk to select
pieces of the output for display.


 Options

  -n n  - line number to output, use 0 for all, 0 by default
  -g    - display group id, off by default
  -o    - display owner, off by default
  -p    - display permissions, off by default
  -d    - display date, off by default
  -f    - display filename on by default

By default, lopt will simply print a list of filenames.

./lopt -n 3 will print the third filename. - Remember this also really
refers to the 4th line of ls -al because we ignore the first line
completely

./lopt -fg -n 3  will printg the group id of the third file.
./lopt -ff should be considered a proper option and should be the same as -f

./lopt -fg-n 3 should produce a message that describes the syntax of
./lopt as -fg-n is not a proper option



All options should be usable on lines by themselves or grouped together.
For example:

./lopt -o -g

and

./lopt -og

and

./lopt -go

should all produce the same output.

The command:

./lopt -g o

should not produce useful output, but rather should describe the valid
outputs.

-n may appear with others on its line for example the following valid
 command

./lopt -gon 3

is a valid command.


The optional inputs are really just selectors from the ls -al
list. Use the "system" function call and awk to produce an ls -al that
has the lines requested above. Do not display the first line of ls
-al.

For example in a sample directory

ls -al
produces:

total 40
drwxr-xr-x   4 sramsey2  staff    136 Sep 21 09:20 .
drwxr-xr-x  12 sramsey2  staff    408 Sep 21 09:20 ..
-rw-r--r--   1 sramsey2  staff    760 Sep 20 22:18 hw1.cpp
-rwxr-xr-x   1 sramsey2  staff  14664 Sep 21 09:20 lopt



./lopt   
produces

.
..
hw1.cpp
lopt


./lopt -p
produces

drwxr-xr-x .
drwxr-xr-x ..
-rw-r--r-- hw1.cpp
-rwxr-xr-x lopt


./lopt -po 
produces

drwxr-xr-x sramsey2	.
drwxr-xr-x sramsey2	..
-rw-r--r-- sramsey2	hw1.cpp
-rwxr-xr-x sramsey2	lopt



./lopt -pog
produces

drwxr-xr-x sramsey2	staff	.
drwxr-xr-x sramsey2	staff	..
-rw-r--r-- sramsey2	staff	hw1.cpp
-rwxr-xr-x sramsey2	staff	lopt


./lopt -pogd
produces

drwxr-xr-x sramsey2	staff	Sep 21 09:20	.
drwxr-xr-x sramsey2	staff	Sep 21 09:21	..
-rw-r--r-- sramsey2	staff	Sep 20 22:18	hw1.cpp
-rwxr-xr-x sramsey2	staff	Sep 21 09:20	lopt


./lopt -pogdf
produces

drwxr-xr-x sramsey2	staff	Sep 21 09:20	
drwxr-xr-x sramsey2	staff	Sep 21 09:21	
-rw-r--r-- sramsey2	staff	Sep 20 22:18	
-rwxr-xr-x sramsey2	staff	Sep 21 09:20


./lopt -pogdfn 2
produces

drwxr-xr-x sramsey2	staff	Sep 21 09:21

./lopt -p -o -g -dfn 2
produces the same output as the previous line. 

I've put tabs in between most fields, except the following: a space
after permissions, and a space between the fields in the date.  You
can put tabs in an awk output command with "\t" but doing this in C++
presents a slight challenge as most of those characters are "escaped".

To get "\t" as a string you would type:
"\"\\t\""

To get spaces, you can use a comma , in awk output.

Feel free to ask questions.
This assignment is due on Sep 30