Merge tab completion improvements from @herr-biber

bash_kernel/kernel.py

@@ -122,17 +122,28 @@ class BashKernel(Kernel):
         if not tokens:
             return default
 
+        matches = []
         token = tokens[-1]
         start = cursor_pos - len(token)
+
+        if token[0] == '$':
+            # complete variables
+            cmd = 'compgen -A arrayvar -A export -A variable %s' % token[1:] # strip leading $
+            output = self.bashwrapper.run_command(cmd).rstrip()
+            completions = set(output.split())
+            # append matches including leading $
+            matches.extend(['$'+c for c in completions])
+        else:
+            # complete functions and builtins
             cmd = 'compgen -cdfa %s' % token
             output = self.bashwrapper.run_command(cmd).rstrip()
+            matches.extend(output.split())
             
-        matches = output.split()
         if not matches:
             return default
         matches = [m for m in matches if m.startswith(token)]
 
-        return {'matches': matches, 'cursor_start': start,
+        return {'matches': sorted(matches), 'cursor_start': start,
                 'cursor_end': cursor_pos, 'metadata': dict(),
                 'status': 'ok'}