One of Yamlfile’s most useful “baked-in” features is run.script.

steps:
  - run:
      script: ./scripts/install-deps.sh
      env:
        DEBIAN_FRONTEND: noninteractive

How it works (without you writing a COPY)#

1. You list the script path in your Yamlfile.
2. Yamlfile reads the file content from your build context (only the script you declared).
3. A temporary scratch layer is created with the script content and executable permissions.
4. The script is mounted read-only into the RUN filesystem at a generated path (e.g. /.yamlfile-script-...).
5. The script is executed directly (or via /bin/sh).

Result: the script runs exactly as if it had been copied in, but it never appears in any layer of the final image unless you later explicitly copy it from the build stage.

This is the moral equivalent of a heredoc RUN <<'EOF' ... or a temporary COPY --from=... that gets cleaned up, but expressed cleanly in YAML.

Comparison to Dockerfile patterns#

Traditional:

COPY scripts/install-deps.sh /tmp/
RUN chmod +x /tmp/install-deps.sh && /tmp/install-deps.sh && rm /tmp/install-deps.sh

Yamlfile:

- run:
    script: scripts/install-deps.sh

Much cleaner — Yamlfile takes care of the temporary mount for you.

See also: Secrets (often used together with scripts that need credentials).