[screen-devel] Scripting Support for Screen

[Sadrul Habib Chowdhury]

Hi. I started working on a lua script loader for screen last night. I am
quite happy with the progress so far. I would like to know what people
think about this kind of work. I discussed about this briefly with Micah
last night, and he also thought discussing this in the list would be
useful.

I will try to answer a few questions that might come up in advance:

* Where is the patchset?
- The current patchset is available at
  http://www.pidgin.im/~sadrul/pp/scripting-lua/. The patches are against
  the development version of screen
  (http://git.savannah.gnu.org/gitweb/?p=screen.git)

* What's the goal?
- The goal right now is to allow executing some user-defined function
  on specific events, e.g. when a window is closed, opened,
  title/position changed, a display is detached etc. etc. easily, i.e.
  without requiring a recompilation/reinstallation.

  I started working on this mostly out of curiosity, to see where it
  goes, and what cool things it might allow users to do. One use I have
  in mind is to send some signal to the process in a window when it's not
  visible in any of the displays, (and send another one when it becomes
  visible for the first time). It doesn't make all that much sense to
  implement such highly personalized features in screen itself.

  I am sure people will find a lot of other interesting things to do.

* Why Lua?
- Because I like it!
  To be perfectly honest, there was no compelling technical reason for me
  to choose lua. I hadn't worked with lua bindings before, but I was told
  it's much easier to work with than with some other scripting languages
  (e.g. python!). I thought I would give it a try and find out.

* Why not guile?
- Because I haven't seen it before, and I wasn't aware of it until Micah
  told me about it last night on IRC!

  Note: with the patchset, it is possible to support multiple scripting
  languages, either built-in at compile time (current), or dynamically
  loaded on demand (not yet implemented, but possible semi-trivially.
  [1] for details). So in theory, it will be possible to have none,
  either or both lua and guile support. (and any other language someone
  cares to write bindings for)

* What about the bloat?
- I would refer to the commit message at [1]

* Is there a sample script?
- Yes! http://www.pidgin.im/~sadrul/pp/scripting-lua/sc.lua
  The 'fore_changed' function towards the end is the one that gets
  executed when the foreground window for a display is changed. It prints
  the list of windows (# and title), a message explaining the switch from
  the previous window to the current one, and finally prints detailed
  information about each display and its foreground window. The display
  information includes the term, tty, user and the canvases.

* What are the current triggers/hooks?
- Right now, only changing the foreground window in a display will
  trigger a function named 'fore_changed' in the lua script. I don't have
  a complete list of hooks in mind yet. I plan on adding new hooks as the
  need arises. Suggestions are very welcome!

I would love to know if people have any opinions, suggestions etc. about
this.

[1] 
http://www.pidgin.im/~sadrul/pp/scripting-lua/0003-Add-a-layer-of-abstraction-for-the-script-bindings.patch

Cheers,
Sadrul