Output from which command for builtins is not following the behavior of bash

[neerfri]

Bug Description

While working on #19 I noticed that the behavior for "which " is different than the expected output of bash.
This is an easy fix but before submitting the PR I wanted to make sure there is no reason for why JustBash behaves this way.
I think this might be confusing to AI agents that will assume they can read the file that which is pointing to but in this case they cannot since it's a builtin.

In bash:

❱ which echo
echo: shell built-in command

In JustBash:

❱ mix run -e 'bash = JustBash.new(); {result, _bash} = JustBash.exec(bash, "which echo"); IO.puts(result.stdout)'
/bin/echo

To Reproduce

bash = JustBash.new()
{result, _} = JustBash.exec(bash, "which echo")
result.stdout
# Expected: "echo: shell built-in command"
# Actual: "/bin/echo"

Expected Behavior

I expect the output of which to follow the behavior of bash. builtins have no path.

Actual Behavior

JustBash fakes a path that does not exist

Environment

• Elixir version: [e.g., 1.17.0]
• OTP version: [e.g., 27.0]
• JustBash version: [e.g., 0.1.0]
• OS: [e.g., macOS 14.0, Ubuntu 22.04]

Additional Context

[ivarvong]

Thanks for the bug report! I fixed this in #22

JustBash.new() |> JustBash.exec("which echo") |> elem(0) |> Map.get(:stdout)
"echo: shell built-in command\n"