Eshell simple echo in parenthesis not working

Question

Why doesn't the following work in eshell

$ (echo "foo")
Symbol's function definition is void: echo

What I tried:
googled eshell parenthesis not working

More Context: Eventually I'm trying to run (source functions.sh; myCoolFunc)

Answer 1

You incorrectly assumed that eshell starts your default shell specified in /etc/passwd but it doesn't, it's a shell on its own:

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 (see Emacs Lisp Interaction) REPL for Emacs and with an interface similar to command shells such as bash, zsh, rc, or 4dos.

The source command you want to run does not work with bash files in eshell as you would expect it but with eshell commands as help mentions:

~ $ source -h
usage: source FILE [ARGS]
Invoke the Eshell commands in FILE in a subshell, binding ARGS to $1,
$2, etc.

    -h, --help           show this usage screen

In order to achieve what you want in eshell buffer you need to start bash manually:

M-x eshell

~ $ bash
$ (echo hi)
hi