Simple Shell

Introduction

This is a simple shell program modeled after the likes of early Unix shells such as the Thompson, Korn or C shells. It was written by Michelle Giraldo and Justin Majetich for a project via Holberton School. The shell provides an interface by which a user may interact with the kernel, as well as a number of built-in tools to ease this interaction. Running in interactive mode, the program solicits a command line from the user via the terminal, parses this input for valid commands, and executes them accordingly. Users may also pipe output from other commands into the shell, causing it to run in non-interactive mode. In this mode, the shell will not prompt the user for input and will automatically exit upon completion of the commands received. For further information regarding functionality and support, refer to the included man page.

Installation

To install our shell on your Linux machine, clone the contents of this repository into a fresh directory and compile with the following command:

gcc -Wall -Werror -Wextra -pedantic *.c -o hsh

Usage

Interactive Mode

user$ ./hsh
$ ls
a.out file0 file1 test.txt
$ 
$ exit
user$ 

Non-Interactive Mode

user$ echo "ls" | ./hsh
a.out file0 file1 test.txt
user$ 

Contents

File	Function	Description
shell.h		contains libraries, function prototypes, externs, and struct declarations
shell.c
	main	directs the shell through its fundamental loop of parsing and executing commands
	receive_sig	prints prompt after user has interrupted loop with "ctrl + c" signal
_getline.c
	_getline	reads input stream into buffer and parses into distinct command lines
	check_buffer	checks if read buffer is empty
	copy_buffer	copies from read buffer up to newline or null-byte
	shift_buffer	shifts read buffer contents left n bytes
_strtok.c
	_strtok	separates tab or space-delimited "words" from the command line into an array of distinct tokens
	count_tokens	counts the number of tokens in a command line
	token_length	takes the length of a given token in a command line
executor.c
	exec_mngr	directs a tokenized command line to either built-in or external execution
	exec_builtin	identify and execute a built-in command
	exec_external	execute a command-specified external program
get_path.c
	get_path	retrieve path values from the "PATH" environment variable
	path_check	determine if argument includes a path
	path_count	count number of paths listed in "PATH" variable
	path_len	take the length of a path
err_mngr.c
	print_err	format and print error message according to error number
	case_three	format error message in case erring built-in function
builtin_exit.c
	builtin_exit	allows user to exit the shell with or without arguments
	_atoi	converts number string to an integer
	is_num	determines if a string is a number
builtin_env.c
	builtin_env	prints the environment
builtin_cd.c
	builtin_cd	parse arguments to determine and call appropriate cd behavior
	cd_HOME	change current directory to home directory
	cd_current	change current directory to current directory
	cd_prev	change current directory to previous directory
	cd_parent	change current directory to parent directory
cd_help.c
	cd_arg	change current directory to path provided as argument
	cd_user	change current directory to user home directory
	get_target	copy path from an environment variable
	set_PWD	set the "PWD" environment variable
	set_OLDPWD	set the "OLDPWD" environment variable
mem_help.c
	alloc_mngr	direct dynamic memory allocations and store a pointer to each in linked list for eventual freeing
	add_mem_node	*add node with pointer to new memory allocation to linked list
	free_mem_list	free linked list of memory allocations
	_realloc	dynamically reallocate memory
	_memset	initialize n bytes of memory to designated value
mem_help_2.c
	free_static_mem_list	free linked list of memory allocations
str_help.c
	_strlen	take the length of a string
	_strncpy	copy n bytes from one string to another
	_strcmp	compare two strings
	_strncmp	compare n bytes of two strings
	_strcat	concatenate one string to another
str_help_2.c
	_revstr	reverse a string
num_help.c
	_itoa	convert integer to string number
	count_digit	count digits in number string