Interacting with Acme

Acme exposes all its innards through a file system structure. Running on a Linux system it’s supposedly possible to use FUSE to have the 9P file system directly available for reading and writing.

Without it, we can interact with Acme through the 9p command, which lets us read and write files on a 9P server. Acme’s files are all found in the acme folder. Each window that Acme has open is assigned a number, the window ID and these are present as folders named by their window IDs. Aside from the window folder, there are some special files and folders that we’ll talk about here.

The index file

The index file is a special file you can read to list all the windows currently open in Acme:

% 9p read acme/index
         15          68         799           0           1 /home/tj/sources/zx50ef/site/interacme.md Del Snarf Undo Put | Look 
          2         105         112           1           0 /home/tj/sources/zx50ef/ Del Snarf Get | Look 
         12          51         348           1           1 /home/tj/sources/zx50ef/site/ Del Snarf Get | Look 
         13          62       11851           0           0 /home/tj/sources/zx50ef/+watch Del Snarf | Look Get Kill Quit 
         14          49         205           0           1 /home/tj/sources/zx50ef/+Errors Del Snarf | Look 

Each line represents a window. For every line, the first number in given is the window ID, so, as an example, we know there exists a folder called acme/15 (in fact the very window in which this is currently being typed!). The second and third numbers are character counts (in runes) in the tag and body, respectively. So acme/15 has 68 characters in the tag, and 799 characters in the body. The fourth number indicates if the window represents a file (0) or folder (1). The last number indicates if the window is modified (1 if true, 0 otherwise).

Window control

For each window, there are a number of ways to interact with them. We can read out the current tag and body, we can save the file, overwrite it, etc.

One could imagine an autosave feature that reads a given window corresponding to an open file, compares the last modified timestamp to the file and issues a Put if a significant amount of time has elapsed, like an autosave.

Creating a new window

We can open a new window like this:

% 9p read acme/new/ctl
         26          18           0           0           0         807 /mnt/font/DroidSans/11a/font          32 

Simply by reading the special acme/new/ctl we get a new window created, and a line including the new window ID back.

Clearing a window

If $winid gives the window id, and we want to clear it:

% echo -n , | 9p write acme/$winid/addr
% echo -n | 9p write acme/$winid/data

The first line selects the entire buffer (the equivalent of executing “Edit ,”). The second line then writes the empty string as the data, overwriting the selection.