* lisp/shell.el (shell-get-old-input-include-continuation-lines): New
defcustom (default nil).
(shell-get-old-input): Like comint-get-old-input-default but include
all continuation lines if the above is true.
(shell-mode): Install shell-get-old-input.  (bug#61069)
* etc/NEWS: Advertise the new defcustom.

diff --git a/etc/NEWS b/etc/NEWS
index 5b8ab06086c..46f0e8bffca 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -163,6 +163,13 @@ this to your configuration:
 After manually editing 'eshell-aliases-file', you can use this command
 to load the edited aliases.
 
+** Shell Mode
+
++++
+*** New variable 'shell-get-old-input-include-continuation-lines'.
+Users can set this variable to tell shell-get-old-input (C-RET) to
+include multiple shell "\" continuation lines from command output.
+
 ** Prog Mode
 
 +++
diff --git a/lisp/shell.el b/lisp/shell.el
index 5cf108bfa3b..31fb98c0176 100644
--- a/lisp/shell.el
+++ b/lisp/shell.el
@@ -366,6 +366,12 @@ shell-has-auto-cd
   :group 'shell-directories
   :version "28.1")
 
+(defcustom shell-get-old-input-include-continuation-lines nil
+  "Whether shell-get-old-input-default includes \"\\\" lines."
+  :type 'boolean
+  :group 'shell
+  :version "30.1")
+
 (defcustom shell-kill-buffer-on-exit nil
   "Kill a shell buffer after the shell process terminates."
   :type 'boolean
@@ -506,6 +512,38 @@ shell--parse-pcomplete-arguments
           (push (mapconcat #'identity (nreverse arg) "") args)))
       (cons (nreverse args) (nreverse begins)))))
 
+(defun shell-get-old-input ()
+  "Default for `comint-get-old-input' in shell-mode.
+If `comint-use-prompt-regexp' is nil, then either
+return the current input field, if point is on an input field, or the
+current line, if point is on an output field.
+If `comint-use-prompt-regexp' is non-nil, then return
+the current line with any initial string matching the regexp
+`comint-prompt-regexp' removed.  In either case, if
+shell-get-old-input-include-continuation-lines is non-nil and the
+current line ends with a backslash, the next line is also included and
+examined for a backslash, ending with a final line without a backslash."
+  (let (field-prop bof)
+    (if (and (not comint-use-prompt-regexp)
+             ;; Make sure we're in an input rather than output field.
+             (not (setq field-prop (get-char-property
+                                    (setq bof (field-beginning)) 'field))))
+        (field-string-no-properties bof)
+      (comint-bol)
+      (let ((start (point)))
+        (cond ((or comint-use-prompt-regexp
+                   (eq field-prop 'output))
+               (goto-char (line-end-position))
+               (when shell-get-old-input-include-continuation-lines
+                 ;; Include continuation lines as long as the current
+                 ;; line ends with a backslash.
+                 (while (and (not (eobp))
+                             (= (char-before) ?\\))
+                   (goto-char (line-end-position 2)))))
+              (t
+               (goto-char (field-end))))
+        (buffer-substring-no-properties start (point))))))
+
 ;;;###autoload
 (defun split-string-shell-command (string)
   "Split STRING (a shell command) into a list of strings.
@@ -642,6 +680,7 @@ shell-mode
   (setq-local font-lock-defaults '(shell-font-lock-keywords t))
   (setq-local shell-dirstack nil)
   (setq-local shell-last-dir nil)
+  (setq-local comint-get-old-input #'shell-get-old-input)
   ;; People expect Shell mode to keep the last line of output at
   ;; window bottom.
   (setq-local scroll-conservatively 101)