🐚 Simple Shell 🐚

Welcome to Simple Shell, a basic UNIX command line interpreter created by Daniel Sarpong and Hiba A. Mohamed. (⌐■_■)

💡 Overview 💡

The Simple Shell is a minimalist UNIX command line interpreter designed for simplicity and ease of use. This shell project includes a collection of C functions to implement a basic shell. The functions are organized into different files based on their functionality.

👨‍💻 Basic Usage 👨‍💻

The shell displays a prompt and waits for the user to type a command. A command line ends with a new line.

$ simple_shell

✍🏻 Command Lines with Arguments ✍🏻

The shell can handle command lines with arguments. Arguments should be separated by spaces.

$ command arg1 arg2

🎯 Handling PATH 🎯

The shell handles the PATH environment variable to locate executable commands.

📋 Built-in Commands 📋

Command	Description
exit	Terminates the shell.
env	Prints the current environment.
setenv	Initializes or modifies an environment variable.
unsetenv	Removes an environment variable.
cd	Changes the current directory of the process.
alias	Prints a list of all aliases or defines new aliases.

🦾 Advanced Features 🦾

• Commands Separator: The shell can handle the ; separator to execute multiple commands.

• Logical Operators: The shell can handle the && and || logical operators.

• Variables Replacement: The shell handles variable replacement for $? and $$.

• Comments: The shell can handle comments denoted by #.

• File Mode: The shell can take a file as a command line argument, executing commands from the file.

  $ simple_shell script.txt
  

🗃️ Files and Functions 🗃️

main.h Header File

Function	Purpose
Header Guards	Ensures single inclusion in the code.
Included Libraries	Standard C libraries for various functionalities.
Macros	Defines BUFFER_SIZE for input buffer size.
Global Variable	extern char **environ for environment variables.
Data Structures	Linked lists for paths, commands, and aliases.
Helper Functions	String manipulation, conversion, tokenization, printing.
Function Prototypes	Declarations for shell functionalities.

Usage:

• Provides a structured foundation for the Simple Shell program, encompassing declarations, macros, and function prototypes.

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main.c Main File

Function	Purpose
main	Entry point for the Simple Shell program.
execute interactively	Enters an infinite loop for interactive mode.
execute batch_file	Executes commands from a batch file.
init path	Initializes the path linked list.
init commands	Initializes the command linked list.
cleanup	Frees allocated memory before exiting.

Usage:

• Handles both interactive and batch modes, parsing and executing commands using the Simple Shell infrastructure.

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display_prompt.c Prompt Function

Function	Purpose
display_prompt	Displays the command prompt ($ ).

Usage:

• Called to show the prompt for the user to input commands in interactive mode.

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reader.c Reading Input Function

Function	Purpose	Return
reader	Reads user input and removes the trailing newline character.	Number of bytes read. -1 on failure.

Usage:

• Utilized to read user input in interactive mode, ensuring a clean input buffer.

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_getline.c Custom Getline Function

Function	Purpose	Parameters	Return
_getline	Reads characters from the specified stream until a newline character is encountered. Dynamically allocates memory for the line buffer.	lineptr: Pointer to the buffer containing the read bytes. n: Number of bytes read and stored in lineptr. stream: Source to read from (usually stdin).	Number of characters read, including the delimiting character but excluding the terminating null byte. -1 on failure.

Usage:

• Utilized to read user input, ensuring dynamic allocation of memory for the line buffer to accommodate varying input lengths.

---

tokenize.c Tokenization Functions

Function	Purpose	Parameters	Return
tokenize	Tokenizes a string into separate arguments dynamically.	input: The string to tokenize.	A pointer to an array of tokenized arguments. NULL on failure.
free_tokenargs	Frees memory allocated for tokenized arguments.	args: The array of tokenized arguments.

Usage:

• tokenize: Utilized for parsing and tokenizing input strings, handling comments denoted by #.
• free_tokenargs: Called to free the memory allocated for the array of tokenized arguments.

---

parse_commands.c Command Parsing Functions

Function	Purpose	Parameters	Return
parse_commands	Parses a line into a linked list of commands, considering command separators.	line: The line to parse.	Pointer to the first command in the linked list.
parse_vector	Parses a vector of commands into a linked list of commands.	argv: The vector of arguments.	Pointer to the first command in the linked list.
create_command	Creates a command and adds it to the linked list of commands.	line: The command string.	Pointer to the header of the linked list.
add_command	Adds a command to a linked list of commands.	new: The command to add.	Pointer to the header of the linked list.
free_commands	Frees a linked list of commands and associated memory.	cmd: Pointer to the linked list.

Usage: These functions collectively handle the parsing, creation, addition, and freeing of command structures in the Simple Shell project.

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_strtok.c Custom Strtok Function

Function	Purpose	Parameters	Return
_strtok	Tokenizes an input string based on a set of delimiter characters. Maintains state between calls to extract subsequent tokens.	s: The input string to be tokenized. d: A string containing delimiter characters.	Returns a pointer to the next token in the string. Returns NULL if no more tokens are found.

Usage:

• Used for parsing strings and extracting tokens based on specified delimiters.
• Maintains state to allow multiple calls for extracting subsequent tokens.

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switch_vars.c Variable Switching Function

Function	Purpose	Parameters	Return
switch_vars	Switches variables in a tokenized string, replacing certain patterns with their corresponding values.	args: Array of tokenized command-line arguments. last_exit_status: Pointer to the last exit status variable.	Returns 1 if replacements are made, 0 otherwise.

Usage:

• Utilized for switching variables in command-line arguments.

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find_separator.c Function

Function	Purpose	Parameters	Return
find_separator	Locates the next command separator in a given string.	line: Pointer to the string to search.	Flag indicating the corresponding separator type. 0 if none, 1 for #, 2 for ;, \n, or \0, 3 for `

Usage:

• Used during command parsing to identify and handle different types of separators.
• Modifies the input string, replacing the found separator with a null terminator.

---

path_functions.c Path Management Functions

Function	Purpose	Parameters	Return
create_paths	Creates a linked list of all paths from the PATH environment variable.	path: Pointer to the head of the paths linked list.	0 on success, 1 on failure.
free_paths	Frees a linked list of paths.	path: Pointer to the head of the paths linked list.
add_path	Adds a path to a linked list of paths.	path: String of the path to be added. head: Pointer to the head of the paths linked list.	0 on success, 1 on failure.
find_path	Checks the PATH for the existence of the first argument's executable.	args: Pointer to parsed arguments. path: Pointer to the head of the paths linked list.	0 on success, 1 on failure.

Usage:

• create_paths initializes the path linked list from the PATH environment variable.
• free_paths releases the memory allocated for the path linked list.
• add_path adds a new path to the linked list.
• find_path checks for the existence of the executable in the specified paths.

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execute_functions.c Command Execution Functions

Function	Purpose	Parameters	Return
execute	Execute a linked list of commands sequentially. Handle command separators like ;, `		, and &&`.
exec_cmd	Execute a single command with arguments. Handle built-in commands, executable files, and custom functions.	cmd: Pointer to the command structure. path: Pointer to the linked list of paths. last_exit_status: Pointer to the exit status of the last command.	Exit status of the executed command.
exec_builtin	Execute built-in commands like exit, env, setenv, unsetenv, and cd.	cmd: Pointer to the command structure. path: Pointer to the linked list of paths.	0 on success, -1 for non-built-in commands.
exec_file	Execute commands from a file.	args: Pointer to the command arguments. path: Pointer to the linked list of paths. last_exit_status: Pointer to the exit status of the last command.	Exit status of the last command.
_fgetline	Reads an entire line from a file descriptor.	lineptr: Pointer to the buffer containing the read bytes. fd: File descriptor to read from.	Number of characters read.
fork_exec	Creates a fork and executes a command.	args: Pointer to the command arguments.	0 on success.
exit_state	Exits the shell in a specified state (with an optional exit code).	cmd: Pointer to the command structure. path: Pointer to the linked list of paths.

Usage:

• execute processes a linked list of commands with separators.
• exec_cmd executes a single command with arguments.
• exec_builtin handles execution of built-in commands.
• exec_file executes commands from a file.
• _fgetline reads a line from a file descriptor.
• fork_exec creates a fork and executes a command.
• exit_state exits the shell in a specified state.

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env.c Environment Functions

Function	Purpose	Parameters	Return
_setenv	Set a new environment variable or modify an existing one.	var: Name of the environment variable. value: Value to set.	Returns 0 on success, 1 on failure.
_unsetenv	Remove an environment variable.	var: Name of the environment variable.	Returns 0 on success, 1 on failure.
print_env	Print environment variables.	None	No return value.
update_path	Update the linked list of paths from the PATH environment variable.	path: Pointer to the head of the paths linked list.	Returns 0 on success, 1 on failure.

Usage:

• _setenv Function:

  • Utilized to set or modify environment variables.

    _setenv("MY_VARIABLE", "my_value");

• _unsetenv Function:

  • Used to remove an environment variable.

    _unsetenv("MY_VARIABLE");

• print_env Function:

  • Called to print all environment variables.

    print_env();

• update_path Function:

  • Updates the linked list of paths from the PATH environment variable.

    update_path(&path);

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_getenv.c Function

Function	Purpose	Parameters	Return	Notes
_getenv	Get the value of an environment variable.	name: Name of the environment variable.	Value of the environment variable, or NULL.	Iterates through environment variables, compares names, extracts values, and allocates memory for the result.

Usage:

• Used to retrieve the value of a specified environment variable.

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cd Function

Function	Purpose	Parameters	Return
_cd	Change the current working directory.	args: Array of arguments containing the new directory.	Returns 0 on success, 1 on failure.

Usage:

• Command syntax: cd [DIRECTORY]
• Change the current working directory using various cases:
  • If the second argument is not provided or is "~", it changes the directory to the home directory.
  • If the second argument is "-", it changes the directory to the previous working directory.
  • Otherwise, it changes the directory to the specified path.
• Uses _getenv to retrieve environment variables for handling "~" and "-" cases.
• Updates the OLDPWD and PWD environment variables after a successful directory change.

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alias_functions.c Alias Management Functions

Function	Purpose	Parameters	Return	Notes
print_all	Print all aliases to stdout.	alias: Head of the linked list of aliases.	None	Iterates through the linked list and prints each alias name and value.
print_spec	Print specific aliases to stdout.	alias: Head of the linked list of aliases.	alias_names: Array of alias names to print.	Iterates through the linked list and prints aliases whose names match the specified array.
define_alias	Define or update an alias.	alias: Head of the linked list of aliases.	name: Name of the alias. value: Value associated with the alias.	Checks if the alias with the given name exists; if yes, updates its value; otherwise, creates a new alias.
unset_alias	Unset an alias.	alias: Head of the linked list of aliases.	name: Name of the alias.	Returns 0 for success, 1 if the alias is not found. Removes the alias with the specified name from the linked list.
free_aliases	Free allocated memory for aliases.	alias: Head of the linked list of aliases.	None	Frees memory for all nodes in the linked list, including name and value strings.

Usage

• alias [name[='value'] ...]: Prints a list of all aliases, one per line, in the form name='value'.
• alias name [name2 ...]: Prints the aliases name, name2, etc., one per line, in the form name='value'.
• alias name='value' [...]: Defines an alias for each name whose value is given. If name is already an alias, replaces its value with value.
• These functions collectively handle the management, printing, definition, and removal of aliases in the Simple Shell.

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_dircat.c Function

Function	Purpose	Parameters	Return	Notes
_dircat	Concatenate a directory pathname to a filename.	dir: Directory path. filename: Filename.	New pointer to the resulting string.	Calculates lengths, checks for a middle slash, allocates memory, and concatenates the directory path and filename. Returns the resulting string.

Usage:

• Utilized for concatenating a directory path to a filename, creating a new string pointer.

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Printing Functions

File	Function	Purpose	Parameters	Return	Details
_print.c	_print	Print a string to standard output.	str: The string to be printed.	N/A	Uses _strlen to determine the string length, writes to standard output using write.
_printchar.c	_printchar	Prints a character.	c: The character to be printed.	Always returns 1 (success).	Writes the character to standard output using write.

Usage:

• _print Function:

  • Utilized to print strings to standard output.

    _print("Hello, World!\n");

• _printchar Function:

  • Used to print individual characters.

    _printchar('A');

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String Manipulation Functions

File	Function	Purpose	Parameters	Return	Details
_strcat.c	_strcat	Concatenate two strings.	dest: Destination string. src: Source string to append.	A pointer to the resulting string.	Appends characters of src to the end of dest.
_strchr.c	_strchr	Locates a character in a string.	s: Pointer to the string. c: Character to find.	A pointer to the first occurrence or NULL.	Finds the first occurrence of c in the string.
_strstr.c	_strstr	Locates a substring in a string.	haystack: String to search. needle: Substring to find.	Returns 0 if substring found, 1 otherwise.	Searches for needle in haystack.
_strlen.c	_strlen	Calculate the length of a string.	str: Input string.	The length of the string.	Counts characters in str until the null terminator.
_strncmp.c	_strncmp	Compare 'n' characters of two strings.	s1: First string. s2: Second string. n: Number of characters to compare.	0 if equal, negative if s1<s2, positive if s1>s2.	Compares first n characters of s1 and s2.
_strcmp.c	_strcmp	Compare two strings.	s1: First string. s2: Second string.	0 if equal, negative if s1<s2, positive if s1>s2.	Compares all characters of s1 and s2.
_cstrcmp.c	_cstrcmp	Compare two strings.	str1: First string. str2: Second string.	0 if equal, negative if str1<str2, positive if str1>str2.	Case-sensitive comparison of str1 and str2.
_strcpy.c	_strcpy	Copy a string from source to destination.	dest: Destination string. src: Source string.	A pointer to the destination string.	Copies characters from src to dest until null terminator.
_strdup.c	_strdup	Duplicates a string.	src: Pointer to the source string.	A pointer to the duplicated string.	Allocates memory and copies content of src.
_itoa.c	_itoa	Converts an integer to a string.	n: Integer to be converted. base: The base for conversion. uppercase: Flag for uppercase format.	A pointer to the resulting string.	Converts n to a string with the specified base and case.
_sstr.c	_sstr	Switches two strings.	dest: Address of the string to be replaced. src: String to replace the old one.	Returns 0 on success, 1 on failure.	N/A
_atoi.c	_atoi	Converts a string to an integer.	s: Pointer to the string to be converted.	The integer value of the string.	Handles negative numbers. Skips leading non-numeric characters. Stops conversion at the first non-numeric character after encountering a digit.

Usage:

These functions collectively aid in manipulating strings, comparing their contents, and converting between different data types, making them valuable helper functions for various operations within the shell implementation.

• _strcat: Concatenate two strings.
• _strchr: Locate a character in a string.
• _strstr: Locate a substring in a string.
• _strlen: Calculate the length of a string.
• _strncmp: Compare 'n' characters of two strings.
• _strcmp: Compare two strings.
• _cstrcmp: Case-sensitive comparison of two strings.
• _strcpy: Copy a string from source to destination.
• _strdup: Duplicate a string.
• _itoa: Convert an integer to a string.
• _sstr: Switch two strings.
• _atoi: Convert a string to an integer.

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🚚 Installation 🚚

1. Clone the repository:

[email protected]:hiba-emording/simple_shell.git

2. Compile the shell:

gcc -Wall -Werror -Wextra -pedantic -std=gnu89 *.c -o simple_shell

3. Run the shell:

./simple_shell

✨ Fun Facts ✨

• The concept of a shell in computing dates back to the early days of Unix in the 1970s.

• The term "shell" comes from the idea that it is the outer layer surrounding the operating system's kernel, providing an interface for users to interact with the system.

• The oldest known shell command is likely the ls command, used for listing directory contents.

• The shell plays a crucial role in the "pipe and filter" philosophy of Unix, allowing commands to be chained together to perform complex operations.

• The design of shells has inspired various scripting languages, including the creation of the widely used Bash scripting language.

• Did you know? The first Unix shell was the Thompson shell, written by Ken Thompson.

• The shell provides a powerful and flexible environment for automation, scripting, and system administration tasks.

• The use of emojis in the command-line interface is a lighthearted way for developers to express themselves in a traditionally text-based environment.

🔁 Share your favorite fun shell fact with the community and let's celebrate the world of command-line interfaces! 🚀 Happy coding! 🌟