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.
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!
Inspiration on this solution
This is the main structure of the program:
void ft_puterror(char *s1, char *s2);
void ft_exec(int ac, char **av, char **ev, int tmpfd)
{
// Set the stdout to tmpfd
// Execve
}
int main(int ac, char **av, char **ev)
{
int tmpfd = dup(STDOUT_FILENO);
while (av[i] && av[i + 1])
{
// Set the start of av as the new cmd to execute
// Count the cmd arguments with ac
// Set i to ac
// Execute the cmd
// if cmd is cd
// chdir
// else if not proceeded by pipe
// Fork execve
// else if proceeded by by pipe
// Pipe fork execve
}
close(tmpfd);
}
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