Subject

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.

Examples

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
• Do not leak file descriptors!

Additional information

For usage just run make.

For exam you only need to write whole code from FOR_EXAM_(WHOLE_CODE_IN_ONE_FILE).c file.