Variable: tramp-user-regexp
tramp-user-regexp is a variable defined in tramp.el.gz.
Value
"[^\"$'-*/:-<>?[-^`{-}[:blank:]]+\\|\\$[_[:alnum:]]+"
Documentation
Regexp matching user names.
Source Code
;; Defined in /usr/src/emacs/lisp/net/tramp.el.gz
(defconst tramp-user-regexp
(rx (| (+ (not (any "/\\^$?*:;|[]{}()<>`'\"" blank)))
;; Environment variable.
(: "$" (+ (any "_" alnum)))))
"Regexp matching user names.")