Added pager settable parameter to control the command used to display paged output

Also:
- ppaged() now uses the pager settable parameter
- By default the pager settable parameter uses the PAGER environment variable if present
- If PAGER environment variable is not present, pager gets set to:
    - "less -SXRF" on POSIX OSes (macOS and Linux)
    - "more" on Windows

1 files changed, 13 insertions, 11 deletions

diff --git a/cmd2/cmd2.py b/cmd2/cmd2.py
index 3d2a8afe..22797430 100644
--- a/cmd2/cmd2.py
+++ b/cmd2/cmd2.py
@@ -385,6 +385,17 @@ class Cmd(cmd.Cmd):
                     break
     feedback_to_output = False  # Do not include nonessentials in >, | output by default (things like timing)
     locals_in_py = False
+    pager = os.environ.get('PAGER')
+    if not pager:
+        if sys.platform.startswith('win'):
+            pager = 'more'
+        else:
+            # Here is the meaning of the various flags we are using with the less command:
+            # -S causes lines longer than the screen width to be chopped (truncated) rather than wrapped
+            # -R causes ANSI "color" escape sequences to be output in raw form (i.e. colors are displayed)
+            # -X disables sending the termcap initialization and deinitialization strings to the terminal
+            # -F causes less to automatically exit if the entire file can be displayed on the first screen
+            pager = 'less -SRXF'
     quiet = False  # Do not suppress nonessential output
     timing = False  # Prints elapsed time for each command
 
@@ -397,6 +408,7 @@ class Cmd(cmd.Cmd):
                 'editor': 'Program used by ``edit``',
                 'feedback_to_output': 'Include nonessentials in `|`, `>` results',
                 'locals_in_py': 'Allow access to your application in py via self',
+                'pager': 'Command used for displaying paged output',
                 'prompt': 'The prompt issued to solicit input',
                 'quiet': "Don't print nonessential feedback",
                 'timing': 'Report execution times'}
@@ -635,17 +647,7 @@ class Cmd(cmd.Cmd):
                 # Don't attempt to use a pager that can block if redirecting or running a script (either text or Python)
                 # Also only attempt to use a pager if actually running in a real fully functional terminal
                 if functional_terminal and not self.redirecting and not self._in_py and not self._script_dir:
-
-                    if sys.platform.startswith('win'):
-                        pager_cmd = 'more'
-                    else:
-                        # Here is the meaning of the various flags we are using with the less command:
-                        # -S causes lines longer than the screen width to be chopped (truncated) rather than wrapped
-                        # -R causes ANSI "color" escape sequences to be output in raw form (i.e. colors are displayed)
-                        # -X disables sending the termcap initialization and deinitialization strings to the terminal
-                        # -F causes less to automatically exit if the entire file can be displayed on the first screen
-                        pager_cmd = 'less -SRXF'
-                    self.pipe_proc = subprocess.Popen(pager_cmd, shell=True, stdin=subprocess.PIPE)
+                    self.pipe_proc = subprocess.Popen(self.pager, shell=True, stdin=subprocess.PIPE)
                     try:
                         self.pipe_proc.stdin.write(msg_str.encode('utf-8', 'replace'))
                         self.pipe_proc.stdin.close()