/simple_shell

A simple shell project for Holberton

Primary LanguageC

simple_shell


Repository Description

This repository contains the files to simulate a basic Unix Shell with its respective commands. It uses the POSIX API to implement many of the same functionalities of the first Ken Thompson's Shell and It is made to carry out the 0x16. C - Simple Shell project at Holberton School.

The predominantly used calls are read, write, open, execve, exit, fflush, fork, free, malloc, getline, isatty, perror, strtok, wait, and waitpid.

This simple shell is a Shell interface written in C programming language that gives to the user a prompt *Hell_Shell>> *, after it accepts, it executes a user inputted command in a separate process called child process.

This shell provides the following features:

  • This program displays a prompt and waits that the user types a command. A command line always ends with a new line (when user push ENTER key).
  • The prompt is displayed again each time a command has been executed.
  • When the user enters exit, Hell shell will end and returns the status 0.
  • When the user enters exit [status], Hell Shell will end and returns the inputted status, where status is a value from 0 to 255.
  • The user could stop the program using Ctrl+D (end of file).
  • The shell handles the command lines with arguments and pathways.
  • The program does not quit when the user imputs ^C (Ctrl+C).
  • The program prints the current enviroment when the user types env.
  • This program executes the most common shell commands as ls, grep, find, pwd, rm, cp, mv, exit, env, history, etc... with arguments.
  • If an executable cannot be found, It prints an error message and displays the prompt again.
  • This Shell supports commentaries using #,
  • The Hell Shell does NOT support wildcard characters such as ls *.dat in parameters (or commands).
  • This shell does NOT support pipes |, shell logical operators as && or ||, neither commands separator ;.

Process Description

The next steps are a brief description about how the shell works:

  1. First, the parent process is created when the user run the program.
  2. Then, the isatty() function using STDIN_FILENO file descriptor -fd- to tests if there is an open file descriptor referring to a terminal. If isatty() returns 1, the prompt is showed using write() with STDOUT_FILENO as fd and waits for an input user command line.
  3. When the user types a command, getline() function reads an entire line from the stream and strtok() function breaks the inputted command into a sequence of non-empty tokens.
  4. Next, it creates a separate child process suing fork() that performs the inputted command. Unless otherwise is specified, the parent process waits for the child to exit before continuing.
  5. After tokening the command, execve() function brings and executes it, the it frees all allocated memory with free().
  6. Finally, the program returns to main process: prints the prompt, and waits for another user input.

Requirements:

General.

  • Allowed editors: vi, vim, emacs
  • All your files will be compiled on Ubuntu 14.04 LTS
  • Your programs and functions will be compiled with gcc 4.8.4 using the flags -Wall -Werror -Wextra and -pedantic
  • All your files should end with a new line
  • A README.md file, at the root of the folder of the project is mandatory
  • Your code should use the Betty style. It will be checked using betty-style.pl and betty-doc.pl
  • Your shell should not have any memory leaks
  • No more than 5 functions per file
  • All your header files should be include guarded

Basic beggining

To run this shell with its respective commands its necessary to clone this reposotory in your terminal. Do it like this:

  • HTTPS:
git clone https://github.com/mecomonteshbtn/simple_shell.git
  • SSH:
git clone git@github.com:mecomonteshbtn/simple_shell.git

Compiling, Debugging and Runing

  • All of your and our programs and functions will be compiled with gcc 4.8.4 using the flags -Wall -Werror -Wextra and -pedantic

  • To compile your functions use: `

gcc -Wall -Wextra -Werror -pedantic -Wno-format -g *.c -o Hell_Shell
  • If you want to debugging the shell, use valgrind:
valgrind --leak-check=full ./Hell_Shell
  • Or just run and try this shell using:
./Hell_Shell
  • This program provides a simple manual to know and get familiar with the shell. Open it by typing:
man ./man_1_simple_shell

Examples

Here are shown some examples of the usage of the Shell:

  • ls
Hell_Shell>> ls
AUTHORS  Hell_Shell  README.md auxiliar_functions.c  create_child.c  dir  execute.c  free_mem.c  generateAUTHORS  man_1_simple_shell  shell.h shell_init.c  tokening.c
Hell_Shell>> /bin/ls
AUTHORS  Hell_Shell  README.md	auxiliar_functions.c  create_child.c  dir  execute.c  free_mem.c  generateAUTHORS  man_1_simple_shell  shell.h shell_init.c  tokening.c
Hell_Shell>> ls -lat
total 88
drwxrwxr-x 4 vagrant vagrant  4096 Apr 16 17:04 .
-rw-rw-r-- 1 vagrant vagrant  5502 Apr 16 17:04 README.md
drwxrwxr-x 2 vagrant vagrant  4096 Apr 16 12:15 dir
drwxrwxr-x 8 vagrant vagrant  4096 Apr 16 00:20 .git
-rw-rw-r-- 1 vagrant vagrant  1964 Apr 15 23:17 shell_init.c
-rw-rw-r-- 1 vagrant vagrant   821 Apr 15 23:17 tokening.c
-rw-rw-r-- 1 vagrant vagrant   756 Apr 15 23:17 free_mem.c
-rw-rw-r-- 1 vagrant vagrant  1911 Apr 15 23:17 shell.h
-rw-rw-r-- 1 vagrant vagrant   702 Apr 15 23:17 create_child.c
-rw-rw-r-- 1 vagrant vagrant  2364 Apr 15 23:17 execute.c
-rwxrwxr-x 1 vagrant vagrant 21729 Apr 15 23:17 Hell_Shell
-rw-rw-r-- 1 vagrant vagrant  1682 Apr 15 23:17 auxiliar_functions.c
-rw-rw-r-- 1 vagrant vagrant  2600 Apr 14 18:25 man_1_simple_shell
-rwxrwxr-x 1 vagrant vagrant   392 Apr 13 14:46 generateAUTHORS
-rw-rw-r-- 1 vagrant vagrant   156 Apr 13 14:46 AUTHORS
drwxrwxr-x 7 vagrant vagrant  4096 Apr  6 18:22 ..
  • pwd
Hell_Shell>> pwd
/home/vagrant/HOLBERTON/simple_shell
  • echo
Hell_Shell>> echo Hello World
Hello World
  • Ctrl+D and Ctrl+C
Hell_Shell>> ^C
Hell_Shell>> 
vagrant@vagrant-ubuntu-trusty-64:~/HOLBERTON/simple_shell$

Node that in the second line the Ctrl+C is typed

Authors: