Custom Shell for Graduate Systems Assignment Creator: Harish Hatmode Email: harish24039@iiitd.ac.in

Overview This is a custom shell developed as part of the Graduate Systems course at IIIT-Delhi. It provides basic shell functionality by leveraging various system calls in C, such as fork(), exec(), waitpid(), and others.

Implementation Details The shell is implemented using the following system calls:

fork(): Creates a child process that is an exact copy of the parent process. execvp(): Replaces the current process with a new process specified by the command. waitpid(): Waits for a specific child process (identified by its PID) to finish execution. dup2(): Duplicates file descriptors, often used for input/output redirection. chdir(): Changes the current working directory of the shell. open(): Opens a file and returns a file descriptor if successful. close(): Closes a file descriptor. Implemented Functions builtIN():

Executes built-in commands such as cd (change directory) and help. formatRedirection():

Handles input and output redirection using < and > operators. commandExecution():

Creates a child process using fork() and executes the given command using execvp(). Handles file descriptors for input/output redirection. parseInput():

Tokenizes the input string entered by the user using strtok() and stores the tokens in a command array for execution. startShell():

Implements the core shell logic to continuously run the shell until the user exits. Calls the above functions to manage different functionalities. main():

The entry point of the program. Initializes and starts the shell. Usage Details This custom shell allows you to:

Execute system commands such as ls, pwd, ps, top, etc. Change directories using the cd command. Get help information using the help command. Execute user-created processes. Handle input/output redirection through < and > operators.