Adds error handling to the pushd and popd builtins. (#52)

Add error handling to the pushd and popd builtins.

This makes them approximately match the behavior of bash,

- Exit `pushd` when too many arguments are passed (instead of simply ignoring extraneous input).
- Fix a bug in `pushd` behavior where the current working directory is pushed onto the stack even if the argument is invalid.

core/builtin.py

@@ -484,9 +484,23 @@ def Cd(argv, mem):


def Pushd(argv, dir_stack):
  dir_stack.append(os.getcwd())
  num_args = len(argv)

  if num_args <= 0:
    util.error('pushd: no other directory')
    return 1
  elif num_args > 1:
    util.error('pushd: too many arguments')
    return 1

  dest_dir = argv[0]
  os.chdir(dest_dir)  # TODO: error checking
  try:
    os.chdir(dest_dir)
  except OSError as e:
    util.error("cd: %r: %s", dest_dir, os.strerror(e.errno))
    return 1

  dir_stack.append(os.getcwd())
  return 0


@@ -496,7 +510,13 @@ def Popd(argv, dir_stack):
  except IndexError:
    log('popd: directory stack is empty')
    return 1
  os.chdir(dest_dir)  # TODO: error checking

  try:
    os.chdir(dest_dir)
  except OSError as e:
    util.error("cd: %r: %s", dest_dir, os.strerror(e.errno))
    return 1

  return 0