Lab 2 Solution

Description

Write a small shell – called shhh – that has the

following capabilities:

1. Can execute a command with the accompanying arguments.

2. Recognize multiple pipe requests and handle them.

3. Recognize redirection requests and handle them.

4. Type “exit” to quit the shhh shell.

Sample commands:

shhh>ls

shhh>ls -t -al

shhh>cat file.txt (file.txt is an existing file)

shhh>ls -al > output.txt

And then open output.txt to see if the content is correct or not

shhh> ls | more | wc

shhh>./pre < input.txt | ./sort > output.txt (./pre and ./sort are the executable from proj1.

input.txt is the file that provides the input

and output.txt is the output file)

shhh> exit

The shell shhh should always wait for ALL the

commands to finish. The topology of the forked processes

should be linear children; e.g the shell should have

as many children as there are processes needed –

with pipes connecting adjacent children.You may assume

that any redirection in the command

is specified like the third example above. E.g.

“redirection in” ( < ) is always specified before

the first pipe appears and “redirection out” ( > )

is always after the last pipe specified. To make

life easier for you, you may assume that only

commands with correct syntax are typed in. In other

words don’t worry about errors in the formation of

the commands.

The partial program is available in TRACS, lab2.c.

The command parsing part is already done in the program.

On your part, you need to implement the above functions.

How to submit?

Zip all your files (including ./pre and ./sort from the last assignment)

and submit to TRACS before the deadline. Homework will NOT be accepted

through emails. You should write a readme textfile telling the grader

how to run your programs. Without this file, it is very likely that your

project will not be run properly.