fossil/venti really are very nice and it is great to have a system that is very easy to hack.

I looked over to check the time and it was the Plan 9 clock, which always takes a second to read. The dots indicating the hours are all the same shape/color, and the hour hand is the same thickness as the minute hand. I figured it'd be trivial to tweak, so I popped up the source. Finding the source is a pain in most Linux distros, but on Plan 9, the location of the source code is at the bottom of the man page. But you don't even need to do that: there's a program called src(1)¹ that can print the location of the source code, or just open it up in your editor². So instead of untarring anything or `apt-get source` or whatever, I just typed `src clock`.

The source was easy to read, about a hundred lines, and I did the tweak and thought "Oh, I should post a patch to fedi, there are people on fedi that use this." But I'd made the changes already, so what do I do to get a diff?

This is the magic part: yesterday(1)³. You type `yesterday $filename` and it mounts the archive (for which you do not need root, because you control your namespace so every mount works like FUSE, and the fileserver enforces permissions itself, so unlike zfs or whatever, any user can securely inspect snapshots and filesystem history) and then prints out the path to that file from yesterday's dump (or whenever, just yesterday is the default). So you can do "diff `{yesterday /sys/src/cmd/clock.c} /sys/src/cmd/clock.c"⁴ and this gives you the diff.

Whole process took about five minutes from wanting to tweak something to installing the new version and retrieving the diff. It was quicker to do than to explain. Nearly everything on Plan 9 is like that, you see something you wanna tweak and you can tweak it with no friction, because the source is simple and available and because of fossil and venti⁵, you can get the full history of arbitrary files.

Here's the diff and a screenshot. (The clock is still nothing impressive but it is somewhat faster to read it; anyway, this is how you do that.)

--

¹ http://man.9front.org/1/src

² The plumber handles this: http://man.9front.org/4/plumber . The overview is that it's sort of like things like OSX's "open" or XDG's (

) "xdg-open", but arbitrary data instead of filenames/URLs only, and the plumber is much more hacker-friendly. So the plumbing file says things like "if it looks like the path to a C file, send it to the 'edit' port" and whatever editor you have open listens for things sent to "edit", sort of like pub-sub. There are also rules in $home/lib/plumbing for starting whatever it is that you want to start, so if there's nothing listening for "plumb to edit" you can tell it how to start up your editor.

³ http://man.9front.org/1/yesterday

⁴ While grabbing the link to the 9front manual, I noticed that the man page also covers `diffy`, which basically does this. I did not know about diffy. Sometimes I post this stuff and someone says "Who cares?" and "Why would you post this?" and that's why. I hope it is useful or interesting to whoever reads it, but trying to explain it is often very useful to me, I find stuff out or it makes me think things through more carefully than just using it.

⁵ I will keep posting this until I am blue in the face: http://doc.cat-v.org/plan_9/4th_edition/papers/venti/ . Here's the fossil paper, too, for good measure: http://doc.cat-v.org/plan_9/4th_edition/papers/fossil/ .
clock.diff
clock.png

~b @torresjrjr@qoto.org

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