0x16. C - Simple Shell

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   | | |_ |/ _` | __/ _ \/ __|  / _ \|  _|  \___ \| '_ \ / _ \ | |
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    \_____|\__,_|\__\___||___/  \___/|_|   |_____/|_| |_|\___|_|_|

The Gates of Shell by Spencer Cheng, featuring Julien Barbier

Resource

• Unix shell
• Thompson shell
• Ken Thompson
• Everything you need to know to start coding your own shell

---

Description

In this project we are tasked with creating our own simple UNIX command interpreter. The 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].

---

Instructions

• Compiling the program: gcc -Wall -Werror -Wextra -pedantic *.c -o hsh

• Interactive mode:

$ ./hsh
($) /bin/ls
hsh main.c shell.c
($)
($) exit
$

• Non-interactie 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
$

---

Example

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Files

File	Description
main.c	entry point for shell
shell.c	executes the shell
shell.h	header
builtins.c	built-in functions
helpers.c	helper functions
extraneous.c	more helper functions
_getenv.c	gets inputted env
search_cwd.c	gets current working dir
find_path.c	finds PATH
bridge.c	checks if builtin or not
execute.c	executes builtin or binary
man_1_simple_shell	man page

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Project Requirements

• All your files will be compiled on Ubuntu 14.04 LTS
• Your C 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
• No more than 5 functions per file
• All your header files should be include guarded
• Use system calls only when you need to

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Tasks

0. README, man, AUTHORS

• Write a (README)[./README.md]
• Write a (man)[./man_1_simple_shell] for your shell.
• You should have an (AUTHORS)[./AUTHORS] file at the root of your repository, listing all individuals having contributed content to the repository.

1. Betty would be proud

• Write a beautiful code that passes the Betty checks

2. Simple shell 0.1

• Write a UNIX command line interpreter.
• Your Shell should:
  • Display a prompt and wait for the user to type a command. A command line always ends with a new line.
  • 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, print an error message and display the prompt again.
  • Handle errors.
  • You have to handle the "end of file" condition (Ctrl+D)

3. Simple shell 0.2

• Handle command lines with arguments

4. Simple shell 0.3

• Handle the PATH

5. Simple shell 0.4

• Implement the exit built-in, that exits the shell
• Usage: exit
• You dont have to handle any argument to the built-in exit

6. Simple shell 1.0

• Implement the env built-in, that prints the current environment

7. What happens when you type ls -l in the shell

• Blog:
  • Medium

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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)

The shell will be compiled this way:

$ gcc -Wall -Werror -Wextra -pedantic -std=gnu89 \*.c -o hsh

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
$

Testing

The shell should work like this in interactive mode:

$ ./hsh
($) /bin/ls
hsh main.c shell.c
($)
($) exit
$

But 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
$

Authors

• Charles Obimnaeto Egesionu

• Jane Nginika