Added ability to query individual alias

Author: kmvanbrunt

cmd2.py

@@ -2745,15 +2745,20 @@ def _cmdloop(self):
     def do_alias(self, arglist):
         """Define or display aliases
 
-Usage:  Usage: alias [<name> <value>]
+Usage:  Usage: alias [name] | [<name> <value>]
     Where:
-        name - name of the alias being added or edited
-        value - what the alias will be resolved to
+        name - name of the alias being looked up, added, or edited
+        value - what the alias will be resolved to (if adding or editing)
                 this can contain spaces and does not need to be quoted
 
     Without arguments, 'alias' prints a list of all aliases in a reusable form which
     can be outputted to a startup_script to preserve aliases across sessions.
 
+    With one argument, 'alias' shows the value of the specified alias.
+    Example: alias ls  (Prints the value of the alias called 'ls' if it exists)
+
+    With two or more arguments, 'alias' creates or replaces an alias.
+
     Example: alias ls !ls -lF
 
     If you want to use redirection or pipes in the alias, then either quote the tokens with these
@@ -2769,8 +2774,16 @@ def do_alias(self, arglist):
             for cur_alias in self.aliases:
                 self.poutput("alias {} {}".format(cur_alias, self.aliases[cur_alias]))
 
+        # The user is looking up an alias
+        elif len(arglist) == 1:
+            name = arglist[0]
+            if name in self.aliases:
+                self.poutput("alias {} {}".format(name, self.aliases[name]))
+            else:
+                self.perror("Alias '{}' not found".format(name), traceback_war=False)
+
         # The user is creating an alias
-        elif len(arglist) >= 2:
+        else:
             name = arglist[0]
             value = ' '.join(arglist[1:])
 
@@ -2785,9 +2798,6 @@ def do_alias(self, arglist):
             self.aliases[name] = value
             self.poutput("Alias created")
 
-        else:
-            self.do_help('alias')
-
     def complete_alias(self, text, line, begidx, endidx):
         """ Tab completion for alias """
         index_dict = \

tests/test_cmd2.py

@@ -1560,6 +1560,16 @@ def test_alias(base_app, capsys):
     out = run_cmd(base_app, 'alias')
     assert out == normalize('alias fake pyscript')
 
+    # Lookup the new alias
+    out = run_cmd(base_app, 'alias fake')
+    assert out == normalize('alias fake pyscript')
+
+def test_alias_lookup_invalid_alias(base_app, capsys):
+    # Lookup invalid alias
+    out = run_cmd(base_app, 'alias invalid')
+    out, err = capsys.readouterr()
+    assert "not found" in err
+
 def test_alias_with_invalid_name(base_app, capsys):
     run_cmd(base_app, 'alias @ help')
     out, err = capsys.readouterr()