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:

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 --.

Run A Cacheable Script

Create scripts/greet.sh in a repository:

#!/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:

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:

./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 when you want to cache existing repository scripts with minimal changes.
• Continue with the Graph guide when you want typed targets, dependencies, and capabilities that Once and coding agents can query.
• Continue with the software development kit overview when an application needs direct access to Once cache primitives.
• Read Infrastructure after the local flow works and you are ready to share cache entries or run actions remotely.