Exam Question

This exam has 1 question, microshell:

• Microshell.c

if you can make this code shorter, but readable, let me know!

Excepted Files

• microshell.c

Subject Text

Allowed functions:

malloc, free, write, close, fork, waitpid, signal, kill, exit, chdir, execve, dup, dup2, pipe, strcmp, strncmp

The Program

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.

Example

for example this should work:

$>./microshell /bin/ls "|" /usr/bin/grep microshell ";" /bin/echo i love my microshell
microshell
i love my microshell
$>

>./microshell 

Hints

• Don't forget to pass the environment variable to execve
• Do not leak file descriptors!

Exam Practice Tool

Practice the exam just like you would in the real exam - https://github.com/JCluzet/42_EXAM