Assignment name  : microshell
Expected files   : *.c *.h
Allowed functions: malloc, free, write, close, fork, waitpid, signal, kill, exit, chdir, execve, dup, dup2, pipe, strcmp, strncmp
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Write a program that will behave like executing a shell command
- The command line to execute will be the arguments of this program
- Executable's path will be absolute or relative but your program must not build a path (from the PATH variable for example)
- You must implement "|" and ";" like in bash
	- we will never try a "|" immediately followed or preceded by nothing or "|" or ";"
- Your program must implement the built-in command cd only with a path as argument (no '-' or without parameters)
	- if cd has the wrong number of argument your program should print in STDERR "error: cd: bad arguments" followed by a '\n'
	- if cd failed your program should print in STDERR "error: cd: cannot change directory to path_to_change" followed by a '\n' with path_to_change replaced by the argument to cd
	- a cd command will never be immediately followed or preceded by a "|"
- You don't need to manage any type of wildcards (*, ~ etc...)
- You don't need to manage environment variables ($BLA ...)
- If a system call, except execve and chdir, returns an error your program should immediatly print "error: fatal" in STDERR followed by a '\n' and the program should exit
- If execve failed you should print "error: cannot execute executable_that_failed" in STDERR followed by a '\n' with executable_that_failed replaced with the path of the failed executable (It should be the first argument of execve)
- Your program should be able to manage more than hundreds of "|" even if we limit the number of "open files" to less than 30.

for example this should work:
$>./microshell /bin/ls "|" /usr/bin/grep microshell ";" /bin/echo i love my microshell
microshell
i love my microshell
$>

Hints:
Don't forget to pass the environment variable to execve

Hints:
Do not leak file descriptors!

>$ valgrind ./a.out "/usr/bin/ls" "-lRa" "|" "/usr/bin/grep" .