#Shell Implementation Overview.#

##This project is a simple shell that provides basic command execution, including built-in commands and support for external programs. Below is a breakdown of key functions and their roles in the shell:##

Core Functions int lsh_num_builtins() Purpose: Returns the count of built-in commands (e.g., cd, help, exit). Why? Helps the shell determine how many internal commands it can process.

int lsh_cd(char ** args) Purpose: Changes the current working directory to the one specified in args[1]. Why? Implements the cd command for navigation.

int lsh_help(char ** args) Purpose: Displays a help message listing all built-in commands and their usage. Why? Provides users with guidance on available shell commands.

int lsh_exit(char ** args) Purpose: Signals the shell to terminate by returning 0. Why? Implements the exit command for quitting the shell.

int lsh_launch(char ** args) Purpose: Forks a child process to execute an external command using execvp(), with the parent process waiting for it to complete. Why? Enables the shell to run external programs.

int lsh_execute(char ** args) Purpose: Determines whether a command is built-in or external. Built-in commands are executed directly, while others are passed to lsh_launch(). Why? Serves as the central execution logic of the shell.

Input Handling char * lsh_read_line(void) Purpose: Reads a line of input from the user using getline(), removes the trailing newline, and returns the string. Why? Ensures efficient reading of user input without a fixed buffer size.

char ** lsh_split_line(char * line) Purpose: Tokenizes a command string into an array of arguments using delimiters ( \t\r\n\a). Why? Necessary for parsing user input and passing arguments to commands.

Shell Execution Loop void lsh_loop(void) Purpose: Implements the shell’s main execution loop, performing the following steps in each iteration: Displays a prompt with the current directory. Reads user input (lsh_read_line()).

Checks for special operators (> for redirection, | for piping). Handles redirection/piping if detected; otherwise, executes the command (lsh_execute()). Why? Provides the core interactive functionality of the shell.

Program Entry Point int main(int argc, char ** argv) Purpose: Initializes the shell and calls lsh_loop() to start execution. Why? Serves as the program’s entry point, as required in C.

System Calls Used The shell utilizes several system calls for process control, file operations, and input handling:

Process management: fork(), execvp(), waitpid(), exit() Directory operations: chdir(), getcwd() File handling: open(), close(), dup2() Pipes and redirection: pipe() Input reading: read() (via getline()) This shell provides a minimal yet functional command-line environment, allowing users to execute both built-in and external commands efficiently.