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.
The most common way to use Clay is to mount a Clay node in a Unix directory. The mounted directory is always at the root of your pier directory.
For more information on Clay, see the Overview, and additional usage information at Using Clay.
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, this means that the command was successful.
A desk is something like an independently revision-controlled branch of your urbit's file-system. Your urbit's system files live in the %base desk.
It's important to note that whenever you want to sync changes from your Unix directory to your ship, you must use the |commit %desk command, where %desk is the desk that you'd like to sync to.
When developing it's a good idea to use a separate desk. Create a %sandbox desk based on the %base desk (our produces your ship name):
~zod:dojo> |merge %sandbox our %base
Most of the time we want to use Clay from Unix. Mount the entire contents of your %sandbox desk to Unix:
~zod: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 use % to mean "current directory." The result of the command below is just like using ls in a Unix terminal.
~zod:dojo> +ls %
Notice how +cat % does the same thing. That's because everything in Clay, including directories, is a file.
Sync from your friend ~bus's %experiment desk to your %sandbox desk:
~zod:dojo> |sync %sandbox ~bus %experiment
If and when your sync is successful, you will receive a message:
kiln: sync succeeded from %experiment on ~bus to %sandbox
The ship that you sync from will get their own message indicating that you're both connected as peers:
; ~zod is your neighbor.
Clay manual
The following constitutes an explanation of handy commands that most Urbit pilots will want to know at some point. Reading this section will get you to the point that you can navigate the file system, sync with Unix, merge your desk, and other basic tasks familiar to novice users of the Unix terminal.
Paths
A path in Clay is a list of URL-safe text, restricted to the characters [a z],[0 9], ., -, _, and ~. This path is a list of strings each prepended by /. 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 three strings indicating the ship, desk, and revision, and might look like /~dozbud-namsep/base/11.
The first 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 %base. The third component is the revision, 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 current ship, desk, and revision is at any given moment by typing % in the Dojo and looking at the first three results. This will display as a cell rather than a path, like
[~.~zod ~.base ~.~2021.3.19..16.11.20..0c60]
Here we see that the revision consists of the date, time, and a short hash.
We use this format 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 %base desk of your ship ~lodleb-ritrul would have a universal address to anyone else on the network: /~lodleb-ritrul/base/186/gen/example/hoon. That, of course, doesn't mean that everyone on the network has privileges to access that path. But given the revision-controlled and immutable nature of Urbit, this means that if the file requested is available, it will always be the same. This means that if an Urbit is serving a webpage, that exact version will always be retrievable (assuming you have access to it).
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.
%s can be stacked to indicate one level further up in the hierarchy for each additional %. Try the following command:
~zod:dojo> %%%
You'll notice that it only has your ship name and the empty list. The two additional %s abandoned the revision 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 of the form /ship/desk/case/path. To switch to the %sandbox desk, you would enter
~sampel-palnet:dojo> =dir /=sandbox=
=dir is used to change the working directory - we will see more on it below.
The above command uses substitution to use your current ship and revision; only the desk argument, which is located between the other two, is given something new. Without substitution, you would need to write:
~sampel-palnet:dojo> =dir /~sampel-palnet/sandbox/85
Substitutions work the same way in the ship/desk/case 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).
~sampel-palnet:dojo> =dir %/gen~sampel-palnet:dojo/=/=/~2021.3.19..16.11.20..0c60/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
~sampel-palnet:dojo/=/=/~2021.3.19..16.11.20..0c60/gen> =dir %/gmail~sampel-palnet:dojo/=/=/~2021.3.19..16.11.20..0c60/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 %base, the following command will produce the same results as the above command.
~sampel-palnet:dojo/=/=/~2021.3.19..16.11.20..0c60/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/base/~2021.3.19..16.11.20..0c60/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 /base/gen/ask is:
~sampel-palnet:dojo> =dir /=base=/gen/ask
This command will turn your prompt into something like this:
~sampel-palnet:dojo/=/=/~2021.3.19..16.11.20..0c60/gen/ask>
Using =dir without anything else uses the null path, which returns you to your base desk.
~sampel-palnet:dojo/=/=/~2021.3.19..16.11.20..0c60/gen/ask> =dir
Your dojo prompt will turn back into ~sampel-palnet:dojo>.
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:
~sampel-palnet:dojo> =dir %/gen~sampel-palnet:dojo/=/=/~2021.3.19..16.11.20..0c60/gen> =dir %%
Revision-control
Mount
Syntax: |mount %/clay/path %mount-point
Mount the /clay/path at the Unix mount point mount-point with your pier as root directory.
Examples:
|mount %/gen %generators
Mounts %/gen to /generators inside your pier directory.
Unmount
|unmount %mount-point
Unmount the the mount point from Unix.
Examples:
|unmount %foo
Unmounts the Unix path /foo.
Merge
|merge %target-desk ~source-ship %source-desk
Merges a source desk into a target desk.
This can optionally include a merge strategy:
|merge %target-desk ~source-ship %source-desk, =gem %strategy
You may also merge a Clay path on your own ship to a desk, along with an optional strategy.
|merge %target-get %/clay/path, =gem %strategy
Examples:
|merge %examples ~wacbex-ribmex %examples
Merge the %examples desk from ~waxbex-ribmex
|merge %work /=base=, =gem %fine
Merge /=base= into %work using merge strategy %fine.
Sync
|sync %target-desk ~source-ship %target-desk
Subscribe to continuous updates from remote desk on local desk.
Examples:
|sync %foo ~dozbud %kids
Unsync
|unsync %target-desk ~source-ship %source-desk
Unsubscribe from updates from remote desk on local desk. Arguments must match original |sync command.
Example:
|unsync %foo ~dozbud %kids
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.
~sampel-palnet:dojo> +cat %/our/base/gen/curl/hoon
|rm
Syntax: |rm path
Remove the data at path. Path must be a path to the 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.