Dojo

The Dojo is our shell; it processes system commands and returns output. It's a good place to quickly experiment with Urbit. On the surface the Dojo is just a Hoon REPL. On the inside, the Dojo is a system for operating on and transforming data in Urbit.

Quickstart

You can use the Dojo to run arbitrary Hoon code, as well as non-Hoon system commands (which begin with :, |, +, -, *, and so forth, as described below).

Math

Evaluate a Hoon expression (whitespace matters):

~your-urbit:dojo> (add 2 2)
~your-urbit:dojo> %+  add  2  2

Tall-form Hoon may require multiple lines:

~your-urbit:dojo> %+  add
~your-urbit:dojo< 2
~your-urbit:dojo< 2

Hoon uses something called the subject. The Dojo has its own subject and that's where Hoon's equivalent of variables, called faces, are stored.

Use =var to save faces to the Dojo subject.

~your-urbit:dojo> =foo (add 2 2)

Note, however, that =var is Dojo syntax, not Hoon syntax. You cannot bind a face in a .hoon file in this way.

System commands

Use =dir to set the current working directory:

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

(% represents your current directory. For a complete explanation on urbit paths, see the filesystem section.)

Generators (files in /gen) are run with +:

~your-urbit:dojo> +hello 'world'

Save output to a file in %clay with *:

~your-urbit:dojo> *some/file/path/hoon 'hello world'

Run system commands from :hood, like reload, using |:

~your-urbit:dojo> |reload %eyre

Generators

Generators are short Hoon scripts, saved as .hoon files in the /gen directory. Many Dojo commands exist in the form of generators. The syntax for running a generator is +genname for a generator saved as genname.hoon in the %base desk. For generators on other desks, you can use the syntax +desk!genname.

+cat

Accepts a path and displays the file. Similar to Unix cat.

~your-urbit:dojo> +cat %/gen/curl/hoon

+code

Generates a code that is used to remotely log into your ship. No arguments.

~your-urbit:dojo> +code

You can change your code to a new randomly generated one by entering |code %reset. Please note that this will prevent Bridge from being able to derive your code in the future.

+ls

Similar to Unix ls. Accepts a path.

~your-urbit:dojo> +ls %/gen
~your-urbit:dojo> +ls /~talsur-todres/base/2/gen/program

+solid

Compile the current state of the kernel and output a noun. Usually downloaded to a file in unix. This generator takes a series of desks to include as its argument. The first desk must be the base desk that contains the Arvo kernel, standard library and related files - typically %base.

~your-urbit:dojo> .urbit/pill +solid %base %garden %landscape %webterm %bitcoin

+tree

Generate a recursive directory listing. Takes a path.

~your-urbit:dojo> +tree %/sys

Hood

The hood is the system daemon. See gen/hood and app/hood.

|hi - Sends a direct message. Sort of like Unix write. Accepts an urbit name (@p) and a string (tape, which is text wrapped with double-quotes).

~your-urbit:dojo> |hi ~binzod "you there?"

|link / |unlink - Link / unlink a CLI app - may or may not be remote. Accepts an optional ship name and a mandatory app name.

~your-urbit:dojo> |link ~talsur-todres %octo

~your-urbit:dojo> |link %chat-cli

|mass - Prints the current memory usage of all the kernel modules. No arguments.

~your-urbit:dojo> |mass

|breload - Reloads a kernel module (vane) from source. Accepts any number of vane names.

~your-urbit:dojo> |breload %clay %eyre

Dojo manual

Sources and sinks

A Dojo command is either a source or a sink. A source is just something that can be printed to your console or the result of some computation. A sink is an effect: a change to the filesystem, a network message, a change to your environment, or a typed message to an app.

Sources can be chained together, but we can only produce one effect per command.

Sinks

= - Set variable

Set any environment variable:

~your-urbit:dojo> =foo 42
~your-urbit:dojo> (add 2 foo)

44

Make sure to note that =var is Dojo syntax, not Hoon syntax. You cannot bind a variable in a .hoon file in this way.

Special variables

There are a few special variables that the Dojo maintains.

: - Send to app

:app goes to a local app, :~ship/app goes to the app on ~ship.

Send a helm-hi message to hood:

~your-urbit:dojo> :hood &helm-hi 'hi'

Apps usually expect marked data, so & is often used here.

* - Save in %clay

Save a new .hoon file in gen:

~your-urbit:dojo> *%/gen/foo/hoon '# hello'

The last component of the path is expected to be the mark (or mime type).

. - Export to Unix

Export a noun to Unix with .:

~your-urbit:dojo> .foo/bar/baz (add 2 2)

Which creates a file at pier/.urb/put/foo/bar.baz.

This is very often used with +solid:

~your-urbit:dojo> .urbit/pill +solid

Which outputs a new urbit.pill to pier/.urb/put/urbit.pill

Sources

_ - Run a function

Use _ to run a gate (or function):

Write an arbitrary function and pass data to it:

~your-urbit:dojo> _|=([a=@] (mul a 3)) 3
9

Use a function to get the status code from an http request:

~your-urbit:dojo> _|=([p=@ud q=* r=*] p) +http://google.com
301

+ - - HTTP requests

+http[s]://example.com - sends a GET request

+http[s]://example.com &json [%s 'hi'] - sends a POST request with the JSON "hi" in the body.

-http[s]://example.com &json [%s 'hi'] - sends a PUT request with the JSON "hi" in the body.

Note that the first of these is a source while the last two are sinks.

+ - Generators

Generators are simple Hoon scripts loaded from the filesystem. They live in gen/.

An example of a generator that is built into your urbit is +code. It produces the code needed to log into your ship remotely.

~your-urbit:dojo> +code
fintyr-haldet-fassev-solhex

Generators on desks other than %base can be run with the syntax +desk!generator.

- - Threads

Threads are transient Hoon processes which are typically invoked by agents, but can also be used in the Dojo. They are located in ted/.

~your-urbit:dojo> -time s3
s3..00a1

Variables

You can use = to set an environment variable in Dojo, but there are a few reserved names that have special uses.

dir

Current working %clay desk and revision. Read / write.

Examples:

~your-urbit:dojo> =dir %/gen
~your-urbit:dojo> +ls %
404/hoon docs/ dojo/hoon lib/ listen/hoon md static/udon talk/ testing/udon tree/main/ unmark/ womb/

now

The current (128-bit @da) time. Read-only.

Example:

~your-urbit:dojo> now
~2016.3.21..21.10.57..429a

our

The current urbit ship. Read-only.

Example:

~your-urbit:dojo> our
~your-urbit

eny

512 bits of entropy. Read-only.

Example:

~your-urbit:dojo> eny
0v27k.n4atp.fovm6.f7ggm.jdkn5.elct5.11tna.4qtid.g4so7.a1h6g.grp7u.qml4i.0ed1v.sl0r0.97d4b.6aepr.6v6qm.ls5ve.60kgb.j6521.2fqcb

Inspecting Values

You can prefix a value in the Dojo with ? to inspect its type in some way.

• ? gives the type as printed by hoon.hoon.
• ?? shows the type noun as-is.
• ??? shows the hoon of the expression.
• ???? reveals the spec of a gate.
• ????? uses an “x-ray” pretty-printer.

> ? `@da`(add ~2000.1.1 ~d366)
  @da
~2001.1.1

> ?? `@da`(add ~2000.1.1 ~d366)
  [%atom %da ~]
~2001.1.1

> ??? `@da`(add ~2000.1.1 ~d366)
[ %ktls
  p=[%sand p=%da q=0]
    q
  [ %ktls
    p=[%sand p=%$ q=0]
      q
    [ %cncl
      p=[%wing p=~[%add]]
        q
      ~[
        [%sand p=%da q=170.141.184.492.615.420.181.573.981.275.213.004.800]
        [%sand p=%dr q=583.330.319.796.472.925.021.798.400]
      ]
    ]
  ]
]

> ???? add
$-([a=@ b=@] @)

> ????? `@da`(add ~2000.1.1 ~d366)
  @da
~2001.1.1

Troubleshooting

%dojo-peer-replaced/%drum-coup-fail

If you carry out a command that crashes the Dojo session (such as a bad scry), Dojo will automatically restart itself with a clean new session. You will lose some Dojo state, such as variables pinned with = or files built with -build-thread.

%dy-edit-busy

If you encounter %dy-edit-busy while entering commands, it is because your Dojo is blocked on a timer or an HTTP request. Type backspace and your Dojo will end the blocked command.