In Emacs Lisp, how to check if a variable is defined?

Question

In Emacs Lisp, how to check if a variable is defined?

Answer 1

you may need boundp: returns t if the variable (character) is not void; more precisely, if its current binding is not empty. It returns zero otherwise.

(boundp 'abracadabra) ; Starts out void. => nil (let ((abracadabra 5)) ; Locally bind it. (boundp 'abracadabra)) => t (boundp 'abracadabra) ; Still globally void. => nil (setq abracadabra 5) ; Make it globally nonvoid. => 5 (boundp 'abracadabra) => t 

Answer 2

In addition to dfa's answer, you can also see if it is related as a function using fboundp :

 (defun baz () ) => baz (boundp 'baz) => nil (fboundp 'baz) => t 

Answer 3

If you want to check the value of a variable from emacs (I don’t know if this is applicable, since you wrote "in Emacs Lisp"?):

M-: launches Eval in the mini-buffer. Write the name of the variable and press return. The mini-buffer shows the value of the variable.

If the variable is not defined, you get a debugger error.

Answer 4

Remember that variables that are nil are considered defined.

 (progn (setq filename3 nil) (boundp 'filename3)) ;; returns t (progn (setq filename3 nil) (boundp 'filename5)) ;; returns nil