Eshell: commands, syntaxes, etc.

Question

Just found that unfinished manual, but it's really unfineshed. Right on the climax. I still don't get it.

• What is that? An eLisp interpreter?
• How do you tell emacs to edit a file from there?
• What is the difference?
• What are the eshell only commands?

Answer 1

Eshell is a command interpreter like a normal shell, but it does not run bash or any other shell underneath. Like bash, it has several types of commands: while bash has aliases, functions, and falls back to $PATH, eshell has aliases, lisp functions, eshell functions, and falls back to $PATH.

So, for example, you can run:

~ $ find-file foo.txt

and the lisp function find-file will be executed non-interactively (unlike M-x), meaning all necessary arguments must be passed in. This is one way to tell emacs to edit a file from eshell. It's probably faster to run C-x C-f, since it will default to the directory that eshell is currently in.

When you run:

~ $ ls

it actually runs the function eshell/ls, which will get a directory listing without calling /bin/ls. There are similar builtins; if you run C-h f eshell/ <TAB> you can get a list of them.

One of the major points of the eshell builtin functions is to make commands fit into other existing emacs functions. For example, grep will go into the *grep* buffer so that you can quickly jump to the results.

It also has aliases, which are somewhat similar to bash aliases, but act a bit like functions in the way they handle arguments. For example, in bash, you might say

alias ll='ls -l'

while in eshell you would say

alias ll ls -l '$*'

and both of those mean the same thing. The $* means basically "expand all arguments", and it's necessary to quote it. You can run alias to see all aliases you've created.