Variable: eshell-lisp-form-nil-is-failure
eshell-lisp-form-nil-is-failure is a customizable variable defined in
esh-cmd.el.gz.
Value
t
Documentation
If non-nil, Lisp forms like (COMMAND ARGS) treat a nil result as failure.
Probably introduced at or before Emacs version 29.1.
Source Code
;; Defined in /usr/src/emacs/lisp/eshell/esh-cmd.el.gz
(defcustom eshell-lisp-form-nil-is-failure t
"If non-nil, Lisp forms like (COMMAND ARGS) treat a nil result as failure."
:type 'boolean)