Wednesday 26 November 2008

Shell features

Here are two features I would like to see in a Unix shell:
  • Timing: The shell should record how long each command takes. It should be able to show the start and stop times and durations of commands I have run in the past.
  • Finish notifications: When a long-running command finishes, the task bar icon for the shell's terminal window should flash, just as instant messaging programs flash their task bar icon when you receive a message. If the terminal window is tabbed, the tab should be highlighted too.
You can achieve the first with the time command, sure, but sometimes I start a command without knowing in advance that it will be long-running. It's hard to add the timer in afterwards. Also, Bash's time builtin stops working if you suspend a job with Ctrl-Z. It would be simpler if the shell collected this information by default.

The second feature requires some integration between the shell and the terminal. This could be done via some new terminal escape sequence or perhaps using the WINDOWID environment variable that gnome-terminal appears to pass to its subprocesses. But actually, I would prefer if the shell provided its own terminal window. There would be more scope for combining GUI and CLI features that way, such as displaying filename completions or (more usefully) command history in a pop-up window.

I have seen a couple of attempts to do that. Hotwire is one, but it is too different from Bash for my tastes. I would like a GUI shell that initially looks and can be used just like gnome-terminal + Bash. Gsh is closer to what I have in mind, but it is quite old, written in Tcl/Tk and C, and not complete.

Saturday 22 November 2008

TempDirTestCase, a Python unittest helper

I have seen a lot of unittest-based test cases written in Python that create temporary directories in setUp() and delete them in tearDown().

Creating temporary directories is such a common thing to do that I have a base class that provides a make_temp_dir() helper method. As a result, you often don't have to define setUp() and tearDown() in your test cases at all.

I have ended up copying this into different codebases because it's easier than making the codebases depend on an external library for such a trivial piece of code. This seems to be quite common: lots of Python projects provide their own test runners based on unittest.

Here's the code:

import shutil
import tempfile
import unittest

class TempDirTestCase(unittest.TestCase):

    def setUp(self):
        self._on_teardown = []

    def make_temp_dir(self):
        temp_dir = tempfile.mkdtemp(prefix="tmp-%s-" % self.__class__.__name__)
        def tear_down():
        return temp_dir

    def tearDown(self):
        for func in reversed(self._on_teardown):