hsh - Simple Shell 💥

hsh is a simple shell program developed as part of our sprint 1 Final project in the Alx Software Engineering programme. This project aims to implement a basic shell that can execute various commands and manage processes in a Unix-like environment allowing users to interact with the operating system. The shell provides a prompt where users can input commands, and it will execute those commands and display the corresponding output.

The purpose of this project is to demonstrate understanding and practical implementation of core concepts in C programming, including process management, file handling (I/O), string manipulation, and command execution.

📖 Learning Objectives

Upon completion of this project, one will have acquired comprehensive knowledge and a deep understanding of the following key concepts:

• Understand the original design and implementation of the Unix operating system.
• Comprehend the functioning of a shell and its role as an interface between the user and the operating system.
• Understanding the concepts of PID (Process ID) and PPID (Parent Process ID) and their significance in process management.
• Gained knowledge about manipulating the environment variables of a process.
• Differentiate between a function and a system call and understand their respective roles.
• Understand the process creation mechanism and the ability to create child processes.
• Recognize the three prototypes of the main function and their specific purposes.
• Understand how the shell utilizes the PATH environment variable to locate executable programs.
• Have good Knowledge of executing another program using the execve system call.
• Understand process management techniques such as suspending the execution of a process until one of its child processes terminates.
• Familiarity with the concept of EOF (End-of-File) and its significance in input/output operations.

Features and functionalities ⚙️

Our hsh shell supports the following features:

• Interactive command line prompt.
• Execution of commands with or without arguments.
• Path resolution to locate executable programs using the PATH environment variable.
• Built-in support for exiting the shell with the exit command.
• Signal handling, allowing termination of processes using Ctrl + D or C.
• setenv: Initialize a new environment variable, or modify an existing one
  • Command syntax: setenv VARIABLE VALUE
  • print something on stderr on failure
• unsetenv: Remove an environment variable
  • Command syntax: unsetenv VARIABLE
  • prints something on stderr on failure

Future Improvements💡

Although this shell implementation provides basic functionality, there are opportunities for further enhancement. Some potential areas for improvement include:

• Implementing more built-in shell commands, such as cd
  • Command syntax: cd [DIRECTORY]
  • If no argument is given to cd, the command must be interpreted like cd $HOME
  • Update the environment variable PWD when you change directory and handle the command cd -
• Implementing more advanced features like I/O redirection and pipes
• Handle command separator ; e.g ($) ls /dir1; ls /dir2

Expected Outputs 🔃

This program has the exact same output as sh (/bin/sh) as well as the exact same error output. The only difference is that when you print an error, the name of the program is equivalent to your argv[0] (See below)

Example of error with sh ⤵️

elgibbor@ubuntu~$ echo "qwerty" | /bin/sh
/bin/sh: 1: qwerty: not found
elgibbor@ubuntu~$ echo "qwerty" | /bin/../bin/sh
/bin/../bin/sh: 1: qwerty: not found
elgibbor@ubuntu~$

Same error with the program hsh ⤵️

elgibbor@ubuntu~$ echo "qwerty" | ./hsh
./hsh: 1: qwerty: not found
elgibbor@ubuntu~$ echo "qwerty" | ./././hsh
./././hsh: 1: qwerty: not found
elgibbor@ubuntu~$

✔ Testing

How it works in interactive mode:

elgibbor@ubuntu~$ ./hsh
($) /bin/ls
hsh main.c shell.c _getevn.c main.h file1
($)
($) exit
elgibbor@ubuntu~$

Then, in non-interactive mode:

elgibbor@ubuntu~$ echo "/bin/ls" | ./hsh
hsh main.c shell.c _getevn.c main.h file1
elgibbor@ubuntu~$
elgibbor@ubuntu~$ cat file1
/bin/pwd
elgibbor@ubuntu~$ cat file1 | ./hsh
/home/elgibbor
elgibbor@ubuntu~$

🧠 Contributors

This project was implemented by Bernard Frimpong and Chiagoziem Elgibbor. Contributions and suggestions are welcome. Feel free to submit a pull request or open an issue on the project repository🤝

Simple shell is not Simple!😩