The CLI

Three commands. Each does a little more than the one before.

Command	Does
opys build	Runs your config and writes a bundle.
opys install	Downloads and unpacks everything. No game.
opys launch	Installs what is missing, then starts the game.

npm install -g @opys/cli

Day to day

opys launch            # try the pack you are working on
opys build             # write the bundle to share
opys launch game.opys --var root=/tmp/test …   # test it as a player

Config or bundle

install and launch take either.

No argument: they read opys.config.mjs, build it into a temporary bundle, and apply your run. This is for you, while making the pack.

A bundle path or URL: they use that bundle as it is. No config is read, so there is no run, and the player's values come from --var. This is what a player does.

opys launch game.opys --var root=/path/to/install --var username=Player \
  --var uuid=00000000-0000-0000-0000-000000000001 --var token=0
opys install https://example.com/packs/game.opys --var root=/path/to/install

A URL is read in pieces, as a launcher reads one: the bundle's directory and manifest, then only the files the installation lacks.

Flags

Flag	Commands	Does
-i, --input	all	Config file. Default opys.config.mjs.
-o, --output	build	Bundle to write. Overrides the config's output.
--mode <name>	all	Passed to the config as mode.
--var key=value	install, launch	Sets a variable. Repeatable.
--feature a,b	install, launch	Switches on a feature, such as java_console.
--log-level <l>	all	silent, error, warn, info, debug.
-h, --help		Prints usage.

Good to know:

• --var wins over the same variable from run.
• A relative -o or output is relative to the config file.
• With no output named at all, build prints the manifest as JSON. Good for reading and diffing, not for installing.

When to use install

It installs the files and stops. Use it to prepare an installation, or in a script that should not start the game.

Forge and NeoForge finish their setup on the player's machine when the game first starts. install does not run the game, so that still happens on the first launch.

Exit codes

Code	Meaning
0	Success.
1	A mistake in the command or config, or a failed build.
2	A download failed.
3	A file did not match its hash.
4	An archive could not be unpacked.
5	The game started, then exited with its own error.

What to do about each: Troubleshooting.