Eshell

To quote the manual

Eshell is a shell-like command interpreter implemented in Emacs Lisp. It invokes no external processes except for those requested by the user. It is intended to be an alternative to the IELM REPL for Emacs and with an interface similar to command shells such as bash, zsh, rc, or 4dos.

Custom Commands

Here are some custom eshell commands I have implemented. Big thanks to this episode of Álvaro Ramírez’s Bending Emacs series for showing me this was possible.

eshell/http-server

A utility command that uses start-process to run Python’s http.server module in the background.

lisp/alc-eshell.el

(require 'alc-python)

(defun eshell/http-server (dirname &rest args)
  "Use `start-process' to invoke a background Python http.server in
the given DIRNAME"
  (let ((port (alc-eshell--get-port-number)))
    (start-process (format "http:%s" port)
                   (format "*http-server<%s>*" dirname)
                   (or python-shell-interpreter "python")
                   "-m" "http.server"
                   "-d" dirname
                   (format "%s" port))
     (browse-url (format "http://localhost:%s" port))))


(defun alc-eshell--get-port-number ()
  (alc-python-one-liner "
import socket

s = socket.socket()
s.bind(('', 0))
print(s.getsockname()[1], end = '')
s.close()"))

Where