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SIMPLE UNIX SHELL Author Osagie Ofunmwegbe Evba

Milestone Project for ALX software engineering Low Level Programming(C) project

DESCRIPTION : Shell was tested on Ubuntu 20.04 LTS system The first trimester's "The gates of shell" project teaches students about the sophisticated ideas that underlie the shell program, such as process, system call, bit manipulation, file management, and error handling. The simple shell (sh) is a UNIX command interpreter that is similar to shell in functionality. The C programming language was used to create this software.

The Gates of Shell”, by Spencer Cheng, featuring Julien Barbier

Resources Read or watch:

Unix shell Thompson shell Ken Thompson Everything you need to know to start coding your own shell concept page man or help:

sh (Run sh as well) Learning Objectives At the end of this project, you are expected to be able to explain to anyone, without the help of Google:

General Who designed and implemented the original Unix operating system Who wrote the first version of the UNIX shell Who invented the B programming language (the direct predecessor to the C programming language) Who is Ken Thompson How does a shell work What is a pid and a ppid How to manipulate the environment of the current process What is the difference between a function and a system call How to create processes What are the three prototypes of main How does the shell use the PATH to find the programs How to execute another program with the execve system call How to suspend the execution of a process until one of its children terminates What is EOF / “end-of-file”? Copyright - Plagiarism You are tasked to come up with solutions for the tasks below yourself to meet with the above learning objectives. You will not be able to meet the objectives of this or any following project by copying and pasting someone else’s work. You are not allowed to publish any content of this project. Any form of plagiarism is strictly forbidden and will result in removal from the program. Requirements General Allowed editors: vi, vim, emacs All your files will be compiled on Ubuntu 20.04 LTS using gcc, using the options -Wall -Werror -Wextra -pedantic -std=gnu89 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 Use system calls only when you need to (why?) Write a README with the description of your project You should have an AUTHORS file at the root of your repository, listing all individuals having contributed content to the repository. Format, see Docker GitHub *There should be one project repository per group. If you and your partner have a repository with the same name in both your accounts, you risk a 0% score. Add your partner as a collaborator. *

More Info Output Unless specified otherwise, your program must have the exact same output as sh (/bin/sh) as well as the exact same error output. The only difference is when you print an error, the name of the program must be equivalent to your argv[0] (See below) Example of error with sh:

$ echo "qwerty" | /bin/sh /bin/sh: 1: qwerty: not found $ echo "qwerty" | /bin/../bin/sh /bin/../bin/sh: 1: qwerty: not found $ Same error with your program hsh:

$ echo "qwerty" | ./hsh ./hsh: 1: qwerty: not found $ echo "qwerty" | ./././hsh ./././hsh: 1: qwerty: not found $

List of allowed 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) _exit (man 2 _exit) fflush (man 3 fflush) fork (man 2 fork) free (man 3 free) getcwd (man 3 getcwd) getline (man 3 getline) getpid (man 2 getpid) isatty (man 3 isatty) kill (man 2 kill) 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 (__xstat) (man 2 stat) lstat (__lxstat) (man 2 lstat) fstat (__fxstat) (man 2 fstat) strtok (man 3 strtok) wait (man 2 wait) waitpid (man 2 waitpid) wait3 (man 2 wait3) wait4 (man 2 wait4) write (man 2 write) Compilation Your shell will be compiled this way:

gcc -Wall -Werror -Wextra -pedantic -std=gnu89 *.c -o hsh Testing Your shell should work like this in interactive mode:

$ ./hsh ($) /bin/lsBut also in non-interactive mode:

$ echo "/bin/ls" | ./hsh hsh main.c shell.c test_ls_2 $ $ cat test_ls_2 /bin/ls /bin/ls $ $ cat test_ls_2 | ./hsh hsh main.c shell.c test_ls_2 hsh main.c shell.c test_ls_2 $ Checks The Checker will be released at the end of the project (1-2 days before the deadline). We strongly encourage the entire class to work together to create a suite of checks covering both regular tests and edge cases for each task. See task 8. Test suite.