`shell-command` output not working when in a function

Question

I have

(shell-command-to-string "ls")

which works just fine but when I put it in a function it breaks as

(defun testing ()
  (shell-command-to-string "ls")
)

outputs nil. I am new to elisp so I am clearly missing something. Can someone point me in the right direction?

Answer 1

In Lisp, a function call is denoted like this: (func arg1 arg2 ...). IOW, the first element of the list is the function and subsequent elements are the (evaluated) arguments. Contrast this with most other languages where a function call is denoted like this: func(arg1, arg2, ...).

So you define the function like this:

(defun testing ()
  (shell-command-to-string "ls")
)

Doing C-x C-e after the closing paren evaluates the defun and adds the definition of the function to the system. Then to call the function you say:

(testing)

This calls the function testing with no arguments.

You should probably read the "Introduction to Programming in Elisp" which can be found here.