Urbit / Docs

Introduction to the Filesystem

Urbit has its own revision-controlled filesystem, Clay. Clay is a typed, global, referentially transparent namespace. An easy way to think about it is like typed git with continuous sync.

The most common way to use Clay is to mount a Clay node in a Unix directory. The Urbit process will watch this directory and automatically record edits as changes, Dropbox style. The mounted directory is always at the root of your pier directory.

Quickstart

This quick-start guide will walk you through some common commands. Follow along using your Dojo. When you get a >= message after entering a command, the means that the command was successful.

When developing it's a good idea to use a separate desk. Create a %sandbox desk based on the %home desk:

|merge %sandbox ~your-urbit %home

Running our produces your ship-name, meaning that you can run the following command instead of typing out the entire thing. Useful for comets, due to their very long names.

|merge %sandbox our %home

Most of the time we want to use Clay from Unix. Mount the entire contents of your sandbox desk to Unix:

~your-urbit:dojo> |mount /=sandbox=

To explore the filesystem from inside Urbit +ls and +cat are useful. +ls displays files in the current directory, and +cat displays the contents of a file.

We can use % to mean “current directory.” The result of the command below is just like using ls in a Unix terminal.

~your-urbit:dojo> +ls %

Notice how +cat % does the same thing. That's because everything in Clay, including directories, is a file.

Let's explore the /web directory of the %sandbox desk.

~your-urbit:dojo> +ls /=sandbox=/web

Let's see the contents of /=sandbox=/web/md:

~your-urbit:dojo> +cat /=sandbox=/web/md

Now let's navigate to that folder using =dir, which is a like cd in Unix.

~your-urbit:dojo> =dir /=sandbox=/web/md

Youl'll notice that your prompt is now ~your-urbit:dojo/sandbox/web/md>. To change back to our home directory, we use =dir without any path.

~your-urbit:dojo/sandbox/web/md> =dir

Sync from your friend ~some-ship's %experiment desk to your %sandbox desk:

|sync %sandbox ~some-ship %experiment

If and when your sync is successful, you will receive a message:

activated sync from %experiment on ~some-ship to %sandbox

The ship that you sync from will get their own message indicating that you're both connected as peers:

; ~your-urbit is your neighbor.

Manual

Paths

A path in Clay is a list of URL-safe text, restricted to the characters [a z],[0 9], ., -, _, and ~. Formally this is a (list knot), meaning that each segment, delineated by /, is of the knot ASCII-text type. In other words, paths are expressed as /foo/bar/baz. File extensions are separated from file names with /, not .. Extensions are syntactically identical to subdirectories, except that they must terminate the path.

Paths begin with a piece of data called a beak. A beak is formally a (p=ship q=desk r=case); it has three components, and might look like /~dozbud-namsep/home/11.

The first beak component is ship, which is, as you might guess, the name of an Urbit ship. The second component is desk, which is a workspace meant to contain other directories; the default desk is %home. The third component is case, which represents version information in various ways: date and time; a version sequence, which is a value incremented by one whenever a file on the given desk is modified; or an arbitrary plaintext label.

You can find what your beak is at any given moment by typing % in the Dojo and looking at the first three results.

We use beaks because, unlike the current internet, the Urbit network uses a global namespace. That means that a file named example.hoon in the /gen directory on the %home desk of your ship ~lodleb-ritrul would have a universal address to anyone else on the network: ~lodleb-ritrul/home/186/gen/example.hoon. That, of course, doesn't mean that everyone on the network has privileges to access that path.

The structure that combines a beak with further path information is called a beam.

Relative paths

The % command, which we gestured at in the above section, represents the relative path, which is the path where you are currently working. If your working directory is just your home desk, indicated by the prompt ~your-planet:dojo>, then running the command below will print your working directory's beam information: your beak, and a ~ that represents the empty list since no path is present.

~your-urbit:dojo> %

%s can be stacked to indicate one level further up in the hierarchy for each additional %. Try the following command:

~your-planet:dojo> %%%

You'll probably notice that it only has your ship name and the empty list. The two additional %s abandoned the case and the desk information by moving up twice the hierarchy.

There are no local relative paths. /foo/bar must be written as %/foo/bar.

Substitution

You don't need to write out the explicit path every time you want to reference somewhere outside of your working directory. You can substitute = for the segments of a path.

Recall that a full address in the the Urbit namespace is a beam: the /ship/desk/case/path. If you've switched to another desk before, you're already familiar with substitution syntax:

~your-urbit:dojo> =dir /=sandbox=

The above command substitutes uses substitution to use your current ship and case; only the desk argument, which is located between the other two, is given something new. Without substitution, you would need to write:

~your-urbit:dojo> =dir /~your-urbit/home/85

Substitutions work the same way in beaks (the ship/desk/case part) and paths. For example, if you are in the /gen directory, you can reference a file in the /app directory like below. (+cat displays the contents of a file).

~your-urbit:dojo/home/gen> +cat /===/app/curl/hoon

Note what was substituted out, and note that we don't need to separate = with /.

If we changed our working directory to something called /gen/gmail, we could access a file called

~fasdul-balsev-lodleb-ritrul:dojo/home/gen/gmail> +cat /===/app/=/split/hoon

Because both paths share a directory named /gmail at the same position in the address hierarchy -- which, if you recall, is just a list -- the above command works!

We can do the same thing between desks. If %sandbox has been merged with %home, the following command will produce the same results as the above command.

~your-urbit:dojo/home/gen/gmail> +cat /=sandbox=/app/=/split/hoon

Most commonly this is used to avoid having to know the current revision number in the dojo: ~lodleb-ritrul/home/~2018.10.2..00.35.44..d7e8/gen/example.hoon

Changing directories

Change the working directory with =dir. It's our equivalent of the Unix cd.

For example, the syntax to navigate to /home/gen/ask is:

~your-urbit:dojo> =dir /=gen=/ask

This command will turn your prompt into something like this:

~your-urbit:dojo/gen/ask>

Using =dir without anything else uses the null path, which returns you to your home desk.

~your-urbit:dojo> =dir

To go up levels in the path hierarchy, recall the relative path expression %. Stacking them represents another level higher in the hierarchy than the current working directory for each % beyond the initial. The command below brings you one level up:

~your-urbit:dojo/gen> =dir %%

Revision-control

Mount

Syntax: |mount /clay/path [Unix-name]

Mount the clay-path at the Unix mount point Unix-name.

Examples:

|mount %/web

Mounts %/web to /web inside your pier directory.

|mount %/gen generators

Mounts %/gen to /generators inside your pier directory.

Unmount
|unmount [clay-path || Unix-name]

Unmount the path or name from Unix.

Examples:

|unmount %/web

Unmounts the path %/web from whatever name it was mounted as.

|unmount %generators

Unmounts the Unix path /generators.

|merge desk beak[, =gem strategy]

Merges a beak into a desk using an optional merge strategy.

A beak is a ship-desk-case triple, encoded as a path(/~dozbud/home/2)

Examples:

|merge %home-work /=home=, =gem %fine

Merge /=home= into %home-work using merge strategy %fine.

|merge %examples ~wacbex-ribmex %examples

Merge the %examples desk from ~waxbex-ribmex

|sync desk plot [plot-desk]

Subscribe to continuous updates from remote plot on local desk. plot-desk can specify the remote desk name. When omitted it is defaulted to being the same as desk. Non-comet urbits have |sync %home ~parent %kids automatically set up (where ~parent is the planet that issued a moon, the star that issued a planet, or the galaxy that issued a star).

Examples:

|sync %home-local ~dozbud %home

|sync %home ~doznec
|unsync desk plot [plot-desk]

Unsubscribe from updates from remote plot on local desk with optional plot-desk. Arguments must match original |sync command.

Example:

|unsync %home-local ~dozbud %home
|label desk name`

Label the current version of desk name.

Example:

|label %home release

Merge strategies

%init - Used if it's the first commit to a desk. Also can be used to “reinitialize” a desk -- revision numbers keep going up, but the new revision isn't necessarily a descendent of the previously numbered version, allowing merges to be rerun.

%this - Keep what's in Bob's desk, but join the ancestry.

%that - take what's in Alice's desk, but join the ancestry. This is the reverse of %this. This is different from %init because the new commit has both sides in its ancestry.

%fine - “fast-forward” merge. This succeeds if and only if one head is in the ancestry of the other.

%meet, %mate, and %meld - find the most recent common ancestor to use as our merge base.

A %meet merge only succeeds if the changes from the merge base to Alice's head (hereafter, “Alice's changes”) are in different files than Bob's changes. In this case, the parents are both Alice's and Bob's heads, and the data is the merge base plus Alice's changed files plus Bob's changed files.

A %mate merge attempts to merge changes to the same file when both Alice and Bob change it. If the merge is clean, we use it; otherwise, we fail. A merge between different types of changes -- for example, deleting a file vs changing it -- is always a conflict. If we succeed, the parents are both Alice's and Bob's heads, and the data is the merge base plus Alice's changed files plus Bob's changed files plus the merged files.

A %meld merge will succeed even if there are conflicts. If there are conflicts in a file, then we use the merge base's version of that file, and we produce a set of files with conflicts. The parents are both Alice's and Bob's heads, and the data is the merge base plus Alice's changed files plus Bob's changed files plus the successfully merged files plus the merge base's version of the conflicting files.

%auto - meta-strategy. Check to see if Bob's desk exists, and if it doesn't we use an %init merge. Otherwise, we progressively try %fine, %meet, and %mate until one succeeds. If none succeed, we merge Bob's desk into a scratch desk. Then, we merge Alice's desk into the scratch desk with the %meld option to force the merge. Finally, we annotate any conflicts, if we know how.

Manipulation

+cat

Syntax: +cat path [path ...]

Similar to Unix cat. +cat takes one or more paths, and prints their contents. If that path is a file, the contents of the file is printed. If the path terminates in a directory, the list of names at that path is produced.

+ls

Syntax: +ls path

Similar to Unix ls. +ls takes a single path.

Produces a list of names at the path.

~your-urbit:dojo> +cat %/our/home/gen/curl/hoon
|rm

Syntax: |rm path

Remove the data at path. path must be a path to actual node, not a 'directory'

|cp

Syntax: |cp to from

Copy the file at from into the path to.

|mv

Syntax: |mv to from

Move the file at from into the path to.

In Clay, |mv is just a shorthand for |cp then |rm. The |rm doesn't happen unless the |cp succeeds.