C - SIMPLE SHELL

A Custom Implementation of a Simple UNIX Command Interpreter.

An ALX SWE Project.

Authors

• @leonardnzekwe
• @rahma-cloud

Features

• Reads, Evalutes, Prints and Loops (REPL)
• Read Command Line Arguments
• Evalute the Arguments
• Print the Evaluted Arguments Output
• Loop Re-Prompting for New Input to Read

Task Roadmap

• Task 0: A beautiful code that passes the Betty checks.
• Task 1: A UNIX command line interpreter.
  • Usage: simple_shell
  • Features:
  • Displays a prompt and waits for the user to type a command.
  • The prompt is displayed again each time a command has been executed.
  • The command lines are simple, no semicolons, no pipes, no redirections or any other advanced features.
  • The command lines are made only of one word. No arguments will be passed to programs.
  • If an executable cannot be found, it prints an error message and displays the prompt again.
  • Executes commands with execve
  • It handles errors with perror
  • It handles the “end of file” condition Ctrl+D
  • Didn't use the PATH, nor implemented any built-ins at this point.
• Task 2: Handling command lines with arguments.
• Task 3: Handling the PATH. Calling fork only if command exits.
• Task 4: Implementing the exit built-in, that exits the shell
  • Usage: exit. Didn't handle any argument to the built-in exit at this point.
• Task 5: Implementing the env built-in, that prints the current environment.
• Task 6: Implementing a custom getline function
  • Features: Uses a buffer to read many chars at once and calls the least possible the read system call. Uses static variables. Doesn't move the cursor.
• Task 7: Implementing a custom strtok function.
• Task 8: Handling arguments for the built-in exit.
  • Usage: exit status, where status is an integer used to exit the shell.
• Task 9: Implement the setenv and unsetenv builtin commands.
• Task 10: Implement the builtin command cd.
• Task 11: Handle the commands separator ;.
• Task 12: Handle the && and || shell logical operators.
• Task 13: Implement the alias builtin command.
• Task 14: Handle variables replacement. Handle the $? variable. Handle the $$ variable.
• Task 15: Handle comments #.
• Task 15: Implement the simple shell taking a file as a command line argument.
  • Usage: simple_shell [filename]
  • The file contains all the commands that the simple shell should run before exiting, one command per line.
  • In this mode, the shell should not print a prompt and should not read from stdin

Files

• _getenv.c: contains the _getenv, a custom definition of the getenv function.
• _printf.c: contains the _printf function and its helper functions, the custom printf is from our implementation of 0x11: C - printf project.
• AUTHORS: contains git log generated list of contributors to the project.
• dup_args.c: contains the dup_args function that duplicates the arguments.
• exe_args.c: conatains the exe_args and free_mem function that executes valid commands and free dynamically allocated memories, respectively.
• even_more_str_funcs.c: contains _isspace _putchar _isdigit functions, which are used for operations on characters & integers.
• exit_shell.c: contains the exit_shell function that exit the shell either with a status code or without.
• get_args.c: contains the get_args REPL base function and check_get_args function that catches the error cases of the get_args function.
• get_line.c: contains get_line function with its helper functions refill_buffer and read_buffer. The get_line is a custom implementation of the C standard getline function.
• main.c: contains the main function, which is the entry point of the program. It also contains the sigint_handler function which gets excutes when the program recieves a SIGINT in the signal std functions.
• main.h: contains all the header files, global variables, macro definition, REPL function protoytpes and string manipulation functions prototypes.
• more_printf_funcs.c: contains more helper functions to the _printf function.
• more_str_funcs: contains _strcmp _strdup _memcpy _strtok _atoi functions, which are used for string manipulation operations.
• print_env.c: contains the print_env function, that prints the environment variables.
• process_args.c: contains process_args, a helper function to get_args function.
• str_funcs: contains _strlen _strcpy strchr strncmp strcat functions, which are used for string manipulation operations.
• tok_args: contains tok_args function, whic is used to tokenise the command line arguments.
• tok_path: contains tok_path function, whic is used to tokenise the enviroment PATH.

Testing Directory

test: contains the text_cmds file, which has some commands that the simple shell should run before exiting, one command per line.

Notes

• Underway Features: setenv unsetenv, cd, ;, && ||, alias, Variables, Comments and File as input; which are task 9, 10, 11, 12, 13, 14, 15, 16 conditons respectively.

Limitations

• The simple shell implementation doesn't yet handle special characters : ", ', `, \, *, &, #
• It's yet to be able to move the cursor