0x16. C - Simple Shell

     _____       _                     __    _____ _          _ _ 
    / ____|     | |                   / _|  / ____| |        | | |
   | |  __  __ _| |_ ___  ___    ___ | |_  | (___ | |__   ___| | |
   | | |_ |/ _` | __/ _ \/ __|  / _ \|  _|  \___ \| '_ \ / _ \ | |
   | |__| | (_| | ||  __/\__ \ | (_) | |    ____) | | | |  __/ | |
    \_____|\__,_|\__\___||___/  \___/|_|   |_____/|_| |_|\___|_|_|

The Gates of Shell by Spencer Cheng, featuring Julien Barbier

Resource

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
$

Features

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.

Builtins

exit - Exit the shell.
env - Print the environment.
setenv - Set an environment variable.
unsetenv - Unset an environment variable.
cd - Change the current directory.
alias - Create an alias.
unalias - Remove an alias.