Add arguments to get the first and last line of text for launch command

docs/changelog.rst

@@ -99,6 +99,10 @@ Detailed list of changes
 - A new action :ac:`scroll_prompt_to_bottom` to move the current prompt
   to the bottom, filling in the window from the scrollback (:pull:`4634`)
 
+- Add two special arguments ``@first-line-on-screen`` and ``@first-line-on-screen``
+  for the :doc:`launch <launch>` command to be used for pager positioning. 
+  (:iss:`4462`)
+
 0.24.2 [2022-02-03]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 

docs/launch.rst

@@ -95,6 +95,12 @@ the command line:
 ``@cursor-y``
     replaced by the current cursor y position with 1 being the topmost cell
 
+``@first-line-on-screen``
+    replaced by the first line on screen. Can be used for pager positioning.
+
+``@last-line-on-screen``
+    replaced by the last line on screen. Can be used for pager positioning.
+
 
 For example::
 

kitty/launch.py

@@ -397,7 +397,7 @@ def launch(
                 elif x == '@line-count':
                     if 'lines' in pipe_data:
                         x = str(pipe_data['lines'])
-                elif x in ('@cursor-x', '@cursor-y', '@scrolled-by'):
+                elif x in ('@cursor-x', '@cursor-y', '@scrolled-by', '@first-line-on-screen', '@last-line-on-screen'):
                     if active is not None:
                         screen = active.screen
                         if x == '@scrolled-by':
@@ -406,6 +406,10 @@ def launch(
                             x = str(screen.cursor.x + 1)
                         elif x == '@cursor-y':
                             x = str(screen.cursor.y + 1)
+                        elif x == '@first-line-on-screen':
+                            x = str(screen.visual_line(0) or '')
+                        elif x == '@last-line-on-screen':
+                            x = str(screen.visual_line(screen.lines - 1) or '')
             final_cmd.append(x)
         exe = which(final_cmd[0])
         if exe: