# Getting Started

This guide installs Once, runs one cacheable script, and shows how to choose
the next path for your repository.

## Installation

Install the current release with [mise](https://mise.jdx.dev/):

```sh
mise use -g "github:tuist/once@$(mise latest github:tuist/once)"
mise exec -- once --version
```

Use `mise use github:tuist/once@...` without `-g` when a repository should
pin its own Once version in `mise.toml`.

The remaining examples assume that mise is active in your shell. If it is
not, prefix each `once` command with `mise exec --`.

## Try an Existing Project

If the repository already uses Cargo, Swift Package Manager, Xcode, or Bazel,
try it before writing Once configuration:

```sh
cd path/to/project
once query targets
once build
once test
once lint
```

Once recognizes the native workspace from its existing files. `once build`,
`once test`, and `once lint` each default to the workspace's own targets: the
build fans out over every workspace-owned target that exposes `build`, the
test run selects first-party tests, and lint runs every workspace-owned
target that exposes `lint`. No `once.toml` is created.

Pass `--all` to any of the three to include targets reached through resolved
dependencies; `once lint --all` in particular will lint vendored third-party
code, so pair it with `--fail-on error` when you want to keep the noise
manageable. Pass `--ui` to `once build` or `once test` on one explicit
target to follow the live graph in the Runs interface. See
[Graph guide](/guide/graph/) for the full workspace-owned rule (and its
current heuristic limitations) and the per-ecosystem behavior.

Continue with the matching guide for [Rust](/guide/graph/rust), [Swift
Packages](/guide/graph/swift-packages), [Xcode
Projects](/guide/graph/apple/xcode), or [Bazel](/guide/graph/bazel) for
prerequisites, native dependency behavior, and current boundaries.

## Run a Cacheable Script

Create `scripts/greet.sh` in a repository:

```sh
#!/usr/bin/env -S once exec -- bash
# once input "../message.txt"
# once output "../build/greeting.txt"
# once cwd ".."

set -eu
mkdir -p build
cp message.txt build/greeting.txt
cat build/greeting.txt
```

Create `message.txt`, make the script executable, and run it:

```sh
printf 'hello from Once\n' > message.txt
chmod +x scripts/greet.sh
./scripts/greet.sh
cat build/greeting.txt
```

The first invocation ends with a trailer containing `cache miss`. Run the
same command again:

```sh
./scripts/greet.sh
```

The second trailer contains `cache hit`. Once reused the recorded result and
restored the declared output without running the script body again.

Change `message.txt` and run the command once more. The input changed, so
Once reports another miss and records the new output.

## What Once Learned

The three `# once` lines form the action contract:

- `input` tells Once which files affect the result.
- `output` tells Once what to capture and restore.
- `cwd` chooses the working directory for the script.

The script itself is also part of the cache key. Changing either the script
or its declared input causes the work to run again.

## Choose Your Next Path

- Continue with [Scripted automation](/guide/scripted/) when you want to
  cache existing repository scripts with minimal changes.
- Continue with the [Graph guide](/guide/graph/) when you want typed targets,
  dependencies, and capabilities that Once and coding agents can query. Its
  [Linting guide](/guide/graph/linting) turns analyzer reports into cacheable,
  normalized findings with an explicit failure policy.
- Continue with the [software development kit overview](/guide/sdk/) when an
  application needs direct access to Once cache primitives.
- Read [Infrastructure](/guide/infrastructure/) after the local flow works
  and you are ready to share cache entries or run actions remotely.