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

Question

score 155 · Accepted Answer · edited Apr 17 '09 at 01:13

155

you may want boundp: returns t if variable (a symbol) is not void; more precisely, if its current binding is not void. It returns nil 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

edited Apr 17 '09 at 01:13

Svante

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answered Apr 16 '09 at 19:06

dfa

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sometimes it might also be useful to use INTERN-SOFT to check whether a symbol exists. – Rainer Joswig Apr 16 '09 at 19:15
I also sometimes use `symbol-value` function to print the actual value. [symbol-value-doc](https://www.gnu.org/software/emacs/manual/html_node/elisp/Accessing-Variables.html#Accessing-Variables). Egs: Using the `eval-expression` command and then typing this out: `(symbol-value 'abracadabra)` – Dhawan Gayash Sep 26 '20 at 19:02
The `let` block returns `nil` for me. Does this work with lexical binding? – HappyFace May 15 '21 at 16:11

Jacob Gabrielson · Answer 2 · 2019-01-28T18:42:50.903

53

In addition to dfa's answer you may also want to see if it's bound as a function using fboundp:

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

edited Jan 28 '19 at 18:42

answered Apr 17 '09 at 15:43

Jacob Gabrielson

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score 4 · Answer 3 · answered Jun 29 '10 at 12:01

4

If you want to check a variable value from within emacs (I don't know if this applies, since you wrote "in Emacs Lisp"?):

M-: starts Eval in the mini buffer. Write in 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.

answered Jun 29 '10 at 12:01

Gauthier

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Equivalently, `M-: (boundp 'the-variable-name) RET` will check without the need for triggering an error. – Resigned June 2023 Dec 25 '16 at 17:42
2

I'm pretty sure the question is about elisp scripts, not the interactive UI of Emacs. – binki Jul 04 '17 at 16:14

cjohansson · Answer 4 · 2018-12-17T08:59:15.740

3

Remember that variables having the value nil is regarded as being defined.

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

(progn (setq filename3 nil) (boundp 'filename5)) ;; returns nil

edited Dec 17 '18 at 08:59

answered Jul 07 '18 at 05:28

cjohansson

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

4 Answers4