brenns10 / lsh

Simple shell implementation. Tutorial here ->

LSH

LSH is a simple implementation of a shell in C, and it is the subject of a tutorial on my website. It demonstrates the basics of how a shell works. That is: read, parse, fork, exec, and wait. Since its purpose is demonstration (not feature completeness or even fitness for casual use), it has many limitations, including:

• Commands must be on a single line.
• Arguments must be separated by whitespace.
• No quoting arguments or escaping whitespace.
• No piping or redirection.
• Only builtins are: cd, help, exit.

Running

Use gcc -o lsh src/main.c to compile, and then ./lsh to run. If you would like to use the standard-library based implementation of lsh_read_line(), then you can do: gcc -DLSH_USE_STD_GETLINE -o lsh src/main.c.

Contributing

Since this is the subject of a tutorial, I'm not looking to extend it with additional features at this time. So I won't be accepting any pull requests that aren't related to bug fixes (and I'm sure there are still bugs in the code!).

However, that doesn't mean that you shouldn't play with the code, make changes, and explore new features! That's the whole point of this project! It's just that other people are doing the same thing, and this project is merely a starting point for your own exploration.

On that note, I would be just tickled if you dropped me a line (see my website for contact info) to show me the cool new features you've added!

License

This code is in the public domain (see UNLICENSE for more details). This means you can use, modify, and distribute it without any restriction. I appreciate, but don't require, acknowledgement in derivative works.

lsh's Issues

Congratulations and Rust version

I really enjoyed testing your lsh and reading the blog post.

FYI & OFFTOPIC: I also created a simple Rust version for fun: https://gist.github.com/rubenrua/55b2ab6757b6c716f05595548784593a

EOF not handled in getline()

I did not know where else to raise an issue regarding the blog post, as getline is not there in the code on github.

The code on the blog post does not handle the case where the user inputs an EOF, wanting to exit the shell. I believe it should be:

char *lsh_read_line(void)
{
  char *line = NULL;
  ssize_t bufsize = 0;  // have getline allocate a buffer for us
  if (getline(&line, &bufsize, stdin) == -1)
    exit(EXIT_SUCCESS);
  return line;
}

Or, to be even more pedantic:

char *lsh_read_line(void)
{
  char *line = NULL;
  ssize_t bufsize = 0;  // have getline allocate a buffer for us

  if (getline(&line, &bufsize, stdin) == -1){
    if (feof(stdin)) {  
      exit(EXIT_SUCCESS);  // We recieved an EOF
    } else  {
      perror("readline");
      exit(EXIT_FAILURE);
    }
  }
  return line;
}

exit in Child process

Why in child process, it exits with EXIT_FAILURE ?
if (execvp(args[0], args) == -1) { perror("lsh"); } exit(EXIT_FAILURE);

I think it should be:
_exit(EXIT_SUCCESS);

Some libc libraries only flush stdout when they see a newline

I compiled your shell against musl libc and then the ">" prompt is missing.

The fix is easy enough:

diff --git a/src/main.c b/src/main.c
index 39b8528..0a705eb 100644
--- a/src/main.c
+++ b/src/main.c
@@ -255,6 +255,7 @@ void lsh_loop(void)

do {
printf("> ");

• fflush(stdout);
  line = lsh_read_line();
  args = lsh_split_line(line);
  status = lsh_execute(args);

Its not working with sftp

I modified user to use it bash shell
usermod -s "binary" username
it does not working, when i change back usermod -s /bin/bash username

it works

Shell gets killed by the kernel

Hi,

If you run the command bash -ic <some_command> the shell gets stopped. Not sure why though, I'm running in the same issue with mine ;(

Contribution to the repository

Hi! Is this project open to contribution?
He never contributes no projects in github, but he caught my attention, it would be a good challenge for me. If you want help, I'm at your disposal.

EOF is not handled properly

Why is the last byte replaced with \0 on EOF?
This makes it impossible to exit the shell using ^D.
A simple fix would be:

if (c == EOF)
    exit(0);

Memory Allocation Error

I believe there is a slight mistake in implementation of realloc function in the main.c at line 182.
Instead of:
buffer = realloc(buffer, bufsize);
The code should have been:
buffer = realloc(buffer, bufsize * sizeof(char));

To express gratitude and ask a small question

I really enjoyed reading this tutorial, I read it all in one go, tried to write the code, and it finally ran successfully.
But I have a small problem is that I did not find any code related to the two commands ls and pwd, but I can use them when launch the program, can you explain why?
Finally, thank you very much for writing this tutorial, it brought me a happy afternoon.

Fix build on Ubuntu clang