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, 15 insertions, 6 deletions

diff --git a/examples/paged_output.py b/examples/paged_output.py
index c56dcb89..72efd4f5 100755
--- a/examples/paged_output.py
+++ b/examples/paged_output.py
@@ -2,26 +2,35 @@
 # coding=utf-8
 """A simple example demonstrating the using paged output via the ppaged() method.
 """
+import os
+from typing import List
 
 import cmd2
 
 
 class PagedOutput(cmd2.Cmd):
-    """ Example cmd2 application where we create commands that just print the arguments they are called with."""
+    """ Example cmd2 application which shows how to display output using a pager."""
 
     def __init__(self):
         super().__init__()
 
     @cmd2.with_argument_list
-    def do_page_file(self, args):
-        """Read in a text file and display its output in a pager."""
+    def do_page_file(self, args: List[str]):
+        """Read in a text file and display its output in a pager.
+
+        Usage: page_file <file_path>
+        """
         if not args:
             self.perror('page_file requires a path to a file as an argument', traceback_war=False)
             return
 
-        with open(args[0], 'r') as f:
-            text = f.read()
-        self.ppaged(text)
+        filename = os.path.expanduser(args[0])
+        try:
+            with open(filename, 'r') as f:
+                text = f.read()
+            self.ppaged(text)
+        except FileNotFoundError as ex:
+            self.perror('ERROR: file {!r} not found'.format(filename), traceback_war=False)
 
     complete_page_file = cmd2.Cmd.path_complete