Support 'comint-pager' in Eshell

* lisp/eshell/esh-var.el (eshell-variable-aliases-list): Add "PAGER".
(eshell-var-initialize): Make 'comint-pager' buffer-local and bind it
in subcommands so that we can temporarily set it as necessary.

* test/lisp/eshell/esh-var-tests.el (esh-var-test/pager-var/default)
(esh-var-test/pager-var/set, esh-var-test/pager-var/unset)
(esh-var-test/pager-var/set-locally): New tests.

* doc/misc/eshell.texi (Variables): Document this (bug#63778).

Co-authored-by: Morgan Smith <Morgan.J.Smith@outlook.com>

1 files changed, 46 insertions, 0 deletions

diff --git a/test/lisp/eshell/esh-var-tests.el b/test/lisp/eshell/esh-var-tests.el
index 3e58fe749dd..ff646f5f977 100644
--- a/test/lisp/eshell/esh-var-tests.el
+++ b/test/lisp/eshell/esh-var-tests.el
@@ -766,6 +766,52 @@ it, since the setter is nil."
    (eshell-match-command-output "echo $INSIDE_EMACS[, 1]"
                                 "eshell")))
 
+(ert-deftest esh-var-test/pager-var/default ()
+  "Test that retrieving the default value of $PAGER works.
+This should be the value of `comint-pager' if non-nil, otherwise
+the value of the $PAGER env var."
+  (let ((comint-pager nil)
+        (process-environment (cons "PAGER=cat" process-environment)))
+    (eshell-command-result-equal "echo $PAGER" "cat")
+    (setq comint-pager "less")
+    (eshell-command-result-equal "echo $PAGER" "less")))
+
+(ert-deftest esh-var-test/pager-var/set ()
+  "Test that setting $PAGER in Eshell overrides the default value."
+  (let ((comint-pager nil)
+        (process-environment (cons "PAGER=cat" process-environment)))
+    (with-temp-eshell
+     (eshell-match-command-output "set PAGER bat" "bat")
+     (eshell-match-command-output "echo $PAGER" "bat"))
+    (setq comint-pager "less")
+    (with-temp-eshell
+     (eshell-match-command-output "set PAGER bat" "bat")
+     (eshell-match-command-output "echo $PAGER" "bat"))))
+
+(ert-deftest esh-var-test/pager-var/unset ()
+  "Test that unsetting $PAGER in Eshell overrides the default value."
+  (let ((comint-pager nil)
+        (process-environment (cons "PAGER=cat" process-environment)))
+    (with-temp-eshell
+     (eshell-insert-command "unset PAGER")
+     (eshell-match-command-output "echo $PAGER" "\\`\\'"))
+    (setq comint-pager "less")
+    (with-temp-eshell
+     (eshell-insert-command "unset PAGER")
+     (eshell-match-command-output "echo $PAGER" "\\`\\'"))))
+
+(ert-deftest esh-var-test/pager-var/set-locally ()
+  "Test setting $PAGER temporarily for a single command."
+  (let ((comint-pager nil)
+        (process-environment (cons "PAGER=cat" process-environment)))
+    (with-temp-eshell
+     (eshell-match-command-output "PAGER=bat env" "PAGER=bat\n")
+     (eshell-match-command-output "echo $PAGER" "cat"))
+    (setq comint-pager "less")
+    (with-temp-eshell
+     (eshell-match-command-output "PAGER=bat env" "PAGER=bat\n")
+     (eshell-match-command-output "echo $PAGER" "less"))))
+
 (ert-deftest esh-var-test/path-var/local-directory ()
   "Test using $PATH in a local directory."
   (let ((expected-path (string-join (eshell-get-path t) (path-separator))))