lab
===
step 1 ▶ open two linux terminal windows

Find the terminal icon in the accessories pulldown
and click on it.  You may have to right-click the
icon for the second terminal window.

step 2 ▶ copy the .pl files to your ~/bin directory

If you don't have a ~/bin directory, use

mkdir bin

in your ~ (home) directory.  Use emacs to copy
the files (see Dr. Shred).  You can also use

cp filepath directory

where cp is the linux command for copy.

step 3 ▶ change the permissions on the .pl files

They should be executable.  First type

cd bin

to make the bin directory your current directory.

Type

sudo chmod +x dr_shred_up.pl
sudo chmod +x dr_shred_mem.pl

The sudo command allows you to issue commands
with root privilege.

step 4 ▶ create the interprocesse communication fifos

You will run two perl programs at the same time which
requires a linux object known as a "fifo" or first-in,
first-out queue.

A queue has the common meaning of a set of objects grouped
in a particular order, like a line at a movie theater.

In this case the objects are the data sent between the two
perl processes.

To create the fifos, type the followin a the linux prompt:

mkfifo mem_ad.ffo
mkfifo mem_da.ffo
mkfifo mem_rw.ffo

mkfifo fifo_name

step 5 ▶ test the fifos

c_1 > c_2 - writes the standard output of c_1 to the
standard input of c_2.  If c_2 is a file or a fifo,
the standard output of c_1 is written the file or fifo.

c_1 < c_2 - writes the standard output of c_2 to the
standard input of c_1.  If c_2 is a file or a fifo, the
data from the file or fifo is read and directed to the
standard input of c_1.

echo string - writes string to the standard output

cat - prints its the standard input

In one of the terminal windows type

echo "1011111" > mem_ad.ffo

This writes to the fifo, assuming the bin directory is
the current directory and

cat < mem_ad.ffo

in the second terminal window.  This reads from the fifo

step 6 ▶ run the perl processes

In one of the terminal windows type

./dr_shred_up.pl

assuming the bin directory is the current directory and

./dr_shred_mem.pl

in the second terminal window.

step 7 ▶ observe the results

You should see

dr_shred_up.pl sending to dr_shred_mem.pl
   "1" to the $rw variable
   "10101010" to the $ad variable

dr_shred_mem.pl sending to dr_shred_up.pl
   "1011111101111111101111111111111011111111110111110111111111111000"
   to the $da variable.