Code a simple shell for Holberton School. This assignment incorporates all topics covered so far, and marks the conclusion of the section of the course that is strictly about learning C programming.

Only use the following functions and system calls:

access (man 2 access)
chdir (man 2 chdir)
close (man 2 close)
closedir (man 3 closedir)
execve (man 2 execve)
exit (man 3 exit)
fork (man 2 fork)
free (man 3 free)
fstat (man 2 fstat)
getcwd (man 3 getcwd)
getline (man 3 getline)
kill (man 2 kill)
lstat (man 2 lstat)
malloc (man 3 malloc)
open (man 2 open)
opendir (man 3 opendir)
perror (man 3 perror)
read (man 2 read)
readdir (man 3 readdir)
signal (man 2 signal)
stat (man 2 stat)
strtok (man 3 strtok)
wait (man 2 wait)
waitpid (man 2 waitpid)
wait3 (man 2 wait3)
wait4 (man 2 wait4)
write (man 2 write)
_exit (man 2 _exit)

Compile like this:

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

The -g is for tracing Valgrind errors

Currently, when run, it looks like this:

vagrant:simple_shell $ ./hsh
Dance Magic Dance
and baby says: cat main.c
#include "shell.h"

int main(void)
{
	reader();
	return(0);
}
and baby says: exit 
vagrant:simple_shell$ 

1. builtins.c - Includes builtin functions:

• is_builtin() - checks to see if the command is a builtin, then returns a function pointer to one of the following functions:
• _exit_with_grace - exits the shell and frees any malloc'd space.
• _env() - prints the current environment.
• _cd() - change pwd. Can be used without arguments. cd - takes the user to the last directory. cd ~ takes the user home.
• help() - Prints help for builtin commands.Not yet built

2. builtins_2.c - Second file with builtin functions:

• _setenv_usr() - User creates or modifies an environment variable.
• _unsetenv_usr() - User deletes an environment variable.Not yet built
• _alias - Sets, modifies or prints an alias. Not yet built
• _history - Prints the history. Clear history with -c flag. Not yet built

3. env_operations.c

• _getenv() - recreation of getenv() from <stdlib.h>. Gets the value of the provided key. Returns NULL if not found or on error.
• _unsetenv() - Unsets an environmental variable. Not yet built. Currently, just returns the output from the standard library.
• _setenv() - Adds or modifies an environmental variable. Not yet built. Currently, just returns the output from the standard library.

4. environment.c - Includes all functions that deal with the environment and linked lists:

• list_from_path - creates a linked list from the PATH variable
• environ_linked_list - creates a linked list from the environ variable. Built, but is not in use yet. Still going to implement.
• search_os() - Search the absolute path provided, search current directory, or search in PATH``

5. executor.c - Includes only one function that is essential to the core functionality

• executor() - Executes a command

6. linked_list_operations.c - Includes general utilities for creating and maintaining linked lists.

• add_node() - Adds a node to a linked list of struct type env_t
• free_list() - Frees a linked list
• print_list() - Prints a linked list

7. main.c - Entry point to program, contains only the opening message and a call to the reader() function.
8. memory_management.c - General utilities related to memory management.

• _realloc - Recreation of realloc from <stdlib.h>. Reallocates space as necessary. Currently works from smaller spaces to larger spaces, or allocates space if NULL is passed. Also sets the unitialized space to '\0'.
• _memset - Fills a memory location with a value for n bytes.
• _memcpy - Copies characters from one place in memory to another for n bytes.

9. parser.c - Includes all string parsing related functions, and includes functions critical to the basic functionality:

• _getline() - Recreation of getline() from <stdio.h>. Gets a line from stdin, delimited by a \n character. Also handles EOF. Returns the line, or NULL on error.
• parser() - Parses a string into tokens. Returns a double pointer.
• is_alias - Filler function for handling aliases. Currently does not do anything. This functionality has not been built.
• global variable flag for signalhandler() - Triggers when ^C is hit, then turns off.
• `sighandler`` - Interrupts the running process if it is not a builtin then prints the prompt again.
• reader() - Reads user input, turns it into a string and parses it into tokens. Then it performs actions based on the first token.

10. shell.h - Header file: Contains all struct definitions, macros, standard library includes, and function prototypes.
11. string_operations.c - Includes all utility functions that deal with string operations:

• _strlen() - Returns the length of a string. Recreation of strlen() from <string.h>
• _strncmp() - Compares two strings for n bytes, and returns the value of the first difference found. Returns 0 when the last value is the same. Recreation of strncmp() from <string.h>
• _strdup() - Duplicates a string. Recreation of strdup() from <string.h>
• _strcat_realloc() - Concatenates two strings and reallocs a space if either one of the strings are too big to fit in the destination.
• _atoi() - Turns a string into an integer. Recreation of atoi() from <stdlib.h>

12. string_operations_2.c - Second file that includes all utility functions that deal with string operations:

• word_count() - Counts words in a string as delimited
• _strlen_const() - same thing as strlen, but accepts const strings.
• simple_print() - Writes to stdout, accepts a const string.
• _isdigit() - Checks to see if a char is a digit. Recreation of isdigit() from <ctype.h>

13. strtok.c - Includes the strtok function, as well as helper functions that do not need to be referenced elsewhere

• _strchr() - Checks for a char in a string. Returns the string on success, and NULL on failure. Recreation of strchr() from <string.h>
• _strspn() - Gets the length of a substring. Recreation of strspn() from <string.h> with a different return type.
• _strpbrk() - search a string for any set of bytes. Recreation of strpbrk()from<string.h>``
• _strtok_r() - Split a string into tokens, and alters the string in the process. Recreation of strtok from <string.h>

14. AUTHORS - List of contributors.
15. LINKS.md - List of links used for learning how to make this project.
16. man_1_simple_shell - Basic manual page.
17. bowie - ASCII art of David Bowie.

• Deal with EOF
• Parser interprets exit -- Currently, if the first 4 characters of the string are exit, the shell will exit. Does it need to call a function to gracefully kill all running processes and exit the program?
• Deal with path
• Build env function

• exit handles arguments to exit -- What is exit status 4?

• Catch ^C (CTRL + C) -- Find the signal and change its behavior.
• Handle ;
• Handle &&, and ||
• Handle # Comments

• getline
• strtok
• getenv
• setenv
• unsetenv

• register builtins before executing commands
• cd
• alias
• help
• history
• Deal with variables
• Scripts as input

• When enter is hit, it segfaults
• When ^C is hit, it stays on one line.
• EOF (^D) it segfaults
• Two unfreed mallocs somewhere. (Check with Valgrind.)
• Only delimiters handled are spaces and newlines.
• Optimization: Change the linked list for path to an array of strings

For a list of resources and commands used, refer to LINKS.md

• Ian Liu-Johnston Personal Website: || Twitter
• David Knoppers LinkedIn || Twitter