Assignment 1: Building a Basic Shell
Professor: Ashutosh Rai
TA: Yash Shirke, Bhavik Sankhla, Aakrity Pandey
Deadline: 11th August 11:59 p.m
Introduction
In this assignment, you will create a basic shell similar to the bash shell in Linux.
Your shell will be responsible for executing user commands, handling pipes
between commands, and implementing some built-in functionalities. Follow the
steps below to complete the assignment:
Objectives
1. Basic Shell Implementation:
• Implement a shell that reads user input and executes commands using
the exec system call.
• The shell should display the prompt "MTL458 >" and continuously
process commands until interrupted by the user.
• Handle errors during command execution by displaying appropriate
error messages.
2. Command Execution:
• Your shell must support executing standard Linux commands such
as ls, cat, echo, and sleep.
3. Pipes:
• Implement support for piping between commands. For example, your
shell should correctly handle a command like grep -o foo file |
wc -l, where the output of one command is used as input to the
next. Assume single pipes only and not multiple pipes.
4. Built-in Commands:
1
• In addition to executing external commands, your shell should sup-
port some built-in commands. Implement the following built-in func-
tionalities:
– cd directoryname: Change the current working directory of the
shell.You can assume the folder names do not contain spaces in
them.
– history: Display the history of commands entered by the user.
5. User Interrupt:
• Ensure that the shell program terminates after receiving the com-
mand exit.
6. Error Handling:
• Ensure that your shell handles incorrect arguments or command for-
mats gracefully. Display error messages without crashing the shell
and continue to prompt for the next command.
Submission
• Submit your source code file in a zipped folder named as your entry number
followed by and assignment1, example: 2020MT60867 assignment1.
• The submission should be in C, and the file should be named entrynumber shell.c.
• Ensure your code is well-commented and follows best practices for read-
ability and maintainability.
Test Cases
Assume the following folder structure in your home directory:
/home/user/
file1.txt
file2.txt
directory1/
file3.txt
directory2/
file4.txt
subdirectory1/
file5.txt
script.sh
Here’s the content of each file for reference:
• file1.txt: Contains the text hello world
2
• file2.txt: Contains the text foo bar
• file3.txt: Contains the text foo foo foo
• file4.txt: Contains the text bar bar bar
• file5.txt: Contains the text foo bar foo
• script.sh: Contains the text echo "This is a script"
1 Test Cases and Expected Outputs
1.1 Basic Command Execution
Test Case 1.1:
Execute a simple command ls
Input: ls
Expected Output:
file1.txt
file2.txt
directory1
directory2
script.sh
Test Case 1.2:
Execute a command with arguments cat file1.txt
Input: cat file1.txt
Expected Output:
hello world
Test Case 1.3:
Execute a command with no arguments echo "Hello"
Input: echo "Hello"
Expected Output:
Hello
1.2 Pipes Between Commands
Test Case 2.1:
Pipe output of ls to grep
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Input: ls | grep file
Expected Output:
file1.txt
file2.txt
script.sh
Test Case 2.2:
Pipe output of cat file2.txt to grep foo
Input: cat file2.txt | grep foo
Expected Output:
foo bar
1.3 Built-in Commands
Test Case 3.1:
Check current directory after cd
Input: pwd
Expected Output:
/home/user/directory2
Test Case 3.2:
Show command history with history
Input: history
Expected Output: A list of recent commands.
Test Case 3.3:
Use cd with invalid directory
Input: cd non_existent_directory
Expected Output:
The File Path Does not exist
Good luck, and happy coding!
