/Custom-Shell-Commands

Primary LanguageC

Custom Shell Commands


Introduction

This is a writeup for the implementation of three custom shell commands (word, dir, and date) in C as part of the IIITD CSE231 course Operating Systems - Assignment 1.

Table of Contents

  1. How to Run the Application
  2. word Command
  3. dir Command
  4. date Command
  5. Compilation and Execution
  6. Error Handling
  7. Conclusion
  8. Contributors

How to run the application

  1. Environment:
    • This program can only run on Linux environment (One of the major reasons being sys/wait.h named c library).
  2. Cloning the Repository:
  3. Opening the Project:
    • Unzip the file.
    • Right-click on the screen and select "Open Terminal here" (or any other similar option).
  4. Running the program:
    • Make sure that your pwd contains the make file!
    • Write the following command on terminal: 
      make install
    • Executable for all the programs have been made.
    • Now, enter the following in terminal: 
      source ~/.bashrc
    • The above command will modify your terminal so you can directly use our 3 customized commands like predefined ones!
  5. Delete executables:
    • To delete all the executables, run the following command on the same terminal: 
      make clean

word Command

Understanding the Code:

The word command is a built-in command that reads the number of words in a text file. The command can also take optional arguments for specific functionality:

  • -n: Ignores new line characters when counting words.
  • -d: Compares word counts between two text files.

Implementation Details:

The word.c program uses file I/O operations to read characters from the given files, counting words based on space and period characters. It supports the specified -n and -d options. For -d, the program compares the word counts of two files and indicates the difference.

Conclusion:

This code effectively calculates word counts in text files while handling various options like ignoring new lines and comparing counts between files. Understanding this code is essential for implementing similar text-processing utilities.


dir Command

Understanding the Code:

The dir command creates a directory and changes the working path to that directory. It can take optional arguments for specific functionality:

  • -r: Removes the directory if it already exists and then creates a new one.
  • -v: Prints messages for each step in the command's execution.

Implementation Details:

The dir.c program uses the mkdir() system call to create directories and the chdir() system call to change the working directory. It handles the optional arguments -r and -v as specified.

Conclusion:

This code effectively manages directories, including options to remove existing directories and display verbose messages. Understanding this code is crucial for implementing directory manipulation utilities.


date Command

Understanding the Code:

The date command returns a file's last modified date and time. It supports optional arguments for specific functionality:

  • -d: Displays the time described by a given string (e.g., '2 days ago', 'tomorrow').
  • -R: Outputs the date and time in RFC 5322 format.

Implementation Details:

The date.c program uses the stat() system call to retrieve file information, including modification time. It handles optional arguments -d and -R as specified. For -d, the program adjusts the time based on the given string and displays the result.

Conclusion:

This code effectively retrieves and formats file modification times, including options for date manipulation and RFC 5322 formatting. Understanding this code is essential for developing time-related utilities in shell scripting.


Compilation and Execution

The shell.c program is the main shell that handles user input and invokes the corresponding command programs based on the provided command names and arguments. It uses the fork() and execvp() system calls to create child processes and execute the specified commands.


Error Handling

The implemented commands include error handling for scenarios such as missing files, incorrect command syntax, and invalid options. Error messages are printed to stderr in case of errors.


Conclusion

The Unix system shell commands (word, dir, and date) have been successfully implemented with C programming. The project demonstrates the use of system calls like fork(), execvp(), and wait() for process management, file operations, and command execution. The error handling ensures graceful handling of various scenarios, providing a reliable user experience. This project showcases the integration of custom shell commands into a Unix-like environment and provides a solid foundation for further exploration and expansion of shell functionalities.


Contributors

Feel free to reach to any of us at sanyam22448@iiitd.ac.in or yash22586@iiitd.ac.in for any questions or issues related to the above assignment.