Assignment name : microshell
Expected files : microshell.c
Allowed functions: malloc, free, write, close, fork, waitpid, signal, kill, exit, chdir, execve, dup, dup2, pipe, strcmp, strncmp
--------------------------------------------------------------------------------------
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!Recreate a simple shell that can execute commands with basic shell features.
malloc,free,write,close,fork,waitpid,signal,kill,exit,chdir,execve,dup,dup2,pipe,strcmp,strncmp
- The program will execute shell commands based on the arguments provided.
- The executable's path will be absolute or relative.
No path resolution using thePATHvariable. - Supports
;(command separator) and|(pipes) like Bash. - Syntax rules:
- No
|immediately followed or preceded by nothing, another|, or;. cdis the only built-in command, and it:- Accepts only a path as an argument (no
-or empty arguments). - Prints an error on incorrect usage:
error: cd: bad arguments - Prints an error if it fails:
error: cd: cannot change directory to path_to_change - Never appears before or after a
|.
- Accepts only a path as an argument (no
- No
- No need to handle wildcards (
*,~, etc.). - No need to manage environment variables (
$VAR).
- If a system call (except
execveandchdir) fails, print:and exit immediately.error: fatal - If
execvefails, print:whereerror: cannot execute executable_that_failedexecutable_that_failedis the failed program.
- The program should handle hundreds of
|pipes, even with a file descriptor limit of< 30.
$> ./microshell /bin/ls "|" /usr/bin/grep microshell ";" /bin/echo i love my microshell
microshell
i love my microshell
$>Run with:
./microshell