MyShell Project - Yoav Sinai

How I Built the Shell

This shell was built using AT&T x64 Assembly. The development process involved the following steps:

1. Initialization: Setting up the basic structure and initializing necessary variables.
2. Input Handling: Reading user input and parsing commands.
3. Execution: Implementing the logic to execute built-in commands and external programs.
4. Error Handling: Adding error messages and handling various edge cases.
5. Testing: Running multiple test cases to ensure the shell works as expected.

Structure of the Project

The project is organized into the following files and directories:

• main.s: The entry point of the shell program, which contains an indefinite loop that runs until the exit command occurs.
• parser.s: Functions for parsing user input and manipulating it.
• executor.s: Functions for forking the process and executing commands.
• string.s: Implementation of some string-related functions.
• constants.s: The constant strings, error codes, error messages, etc.
• cd.s: Implementation of the cd command in the shell.
• exit.s: Implementation of the exit command in the shell (exits from it).
• errors.s: Handles errors and prints the details to stderr.
• Makefile: Script to compile the project.
• README.md: Documentation of the project.

Decision Process

Implementation Steps:

1. Basic Input Reading: Initially, the project started with implementing the basic functionality to read user input.
2. Command Execution: After successfully reading input, the next step was to execute commands.
3. Error Handling: Once command execution was in place, error handling was introduced using a switch table method with custom error codes.
4. Project Restructuring: To improve maintainability and readability, the project was restructured by splitting it into multiple files, making it more modular instead of having one long file.

Detailed Summary of Error Messages and Codes

The shell handles various errors and provides the following messages and codes:

• Command/File/Directory Not Found: If a command/file/dir is not found, the shell prints Error: No such file or directory and continues.
• Empty Command: If the user inputs an empty command, the shell prints Error: Empty command and continues.
• Permission Denied: If a command cannot be executed due to permission issues, the shell prints Error: Permission denied and continues.
• Execution Failure: If a command fails to execute, the shell prints Error: Execution failed.

These error messages and codes help in diagnosing issues and understanding the shell's behavior.

Additional Information

• Redirections: The shell does not support redirections (< and > operators).
• Piping: The shell does not support piping (| operator).
• Maximum Command Length: The maximum length of a command is 1024 characters.