Question

M-x < TAB > prints all the defined functions.

To check a variable is defined or not evaluating the following expression,
(boundp ‘variable-name) C-x C-e will print t if the variable-name is defined else nill.

How to print all the defined variables in emacs.

Answer 1

It’s unclear exactly what you want to do with a full list of symbols, since the way in which M-x displays function names is somewhat specialized.

Assuming that you want to programmatically obtain a list of all defined symbols, here’s how auto-complete.el does it:

(loop for x being the symbols
    if (boundp x)
    collect (symbol-name x))

Note that you can also enter M-x describe-var RET, and then press TAB to get a sorted completion list of all symbols.