alusta 2026.6.28

Detect the current platform: OS family, flavor, and CPU architecture.

alusta

Platform (Finnish: alusta) - detect the current platform: OS family, flavor, and CPU architecture.

Reports results as human-readable text, JSON, or shell export statements. An embedded DSL lets scripts assert platform constraints and branch on the result via exit code alone.

Requires Python 3.11 or later.

Install

pip install alusta

Manual

The man page provides the CLI reference (man alusta after placing the file on your MANPATH)

To use man alusta, copy docs/alusta.1 to a directory on your MANPATH, for example:

mkdir -p ~/.local/share/man/man1
cp docs/alusta.1 ~/.local/share/man/man1/

Quickstart

Run alusta with no arguments for a compact plain-text summary:

$ alusta
family=linux
flavor=linux
arch=x86_64
  distro=ubuntu

For a dedicated feature walkthrough you can follow in minutes visit quickstart. A step-by-step guided build of a running registry is provided in the tutorial.

Output formats

JSON

--json prints a schema-validated JSON document, pretty-printed by default. --compact collapses it to a single line; --pretty makes the default explicit.

alusta --json
alusta --json --compact

Shell export

--export prints POSIX export statements for eval:

eval $(alusta --export)
echo $ALUSTA_FAMILY   # linux
echo $ALUSTA_FLAVOR   # linux
echo $ALUSTA_ARCH     # x86_64

Detail keys are uppercased and prefixed with ALUSTA_; hyphens in key names become underscores.

Detection signals

--explain augments the output with the raw signals used to determine the platform — file contents, environment variables, and syscall results. Works with both plain text and --json.

Assertions

--assert EXPR evaluates a DSL expression against the detected platform. Exits 0 if the expression is true, 1 if false, 2 on a parse or semantic error.

alusta --assert "family=linux"
alusta --assert "family=linux and arch=x86_64"
alusta --assert "flavor in (linux, wsl)"
alusta --assert "flavor=wsl and detail.wsl_version=2"
alusta --assert "family not in (windows, macos)"

Add --quiet to suppress all output and rely on the exit code alone:

if alusta --quiet --assert "family=linux"; then
    echo "on Linux"
fi

DSL reference

Fields: family, flavor, arch, detail.KEY.

Operators:

• field = value or field == value — equality
• field != value — inequality
• field in (v1, v2, ...) — membership
• field not in (v1, v2, ...) — non-membership
• not expr — logical negation
• expr and expr — logical conjunction (lower precedence than not)
• expr or expr — logical disjunction (lower precedence than and)
• (expr) — grouping

Values are unquoted words composed of alphanumerics and _, -, .. Whitespace around operators is ignored.

Single-field output

--field NAME prints the value of one field and exits:

alusta --field family          # linux
alusta --field arch            # x86_64
alusta --field detail.distro   # ubuntu

Combine with --json to receive the value as a JSON-encoded scalar. Exits 1 if detail.KEY is requested but absent on this platform.

JSON schema

--schema prints the embedded JSON schema for the output document.

Platforms and detail keys

Family	Flavor	Detail keys
linux	linux	distro, distro_version
linux	wsl	wsl_version, wsl_name, distro, distro_version
windows	windows	windows_version
windows	msys	msystem
windows	cygwin	—
macos	macos	macos_version

Detail keys are omitted when not available on the current system.

Exit codes

• 0 — success; for --assert, the expression is true; for --field, the key was found and printed.
• 1 — for --assert, the expression is false; for --field, detail.KEY is absent on this platform.
• 2 — error: unknown flag, invalid --assert expression, or JSON schema validation failure.

Python API

alusta exposes its detection and assertion logic as a library:

from alusta import detect, evaluate, validate

info = detect()
print(info.family, info.flavor, info.arch)
print(info.detail)    # dict of flavor-specific keys, may be empty
print(info.signals)   # raw detection signals used to determine the platform

result = evaluate("family=linux and arch=x86_64", info)  # True or False

errors = validate({"family": info.family, "flavor": info.flavor, "arch": info.arch})
# empty list means valid

detect() accepts keyword-only injection arguments for deterministic testing: _sys_platform, _machine, _environ, _proc_version, _os_release, _mac_ver, _win_ver.

Design and requirements

Document	Identifier	File
Software Requirements Specification	ALU-SRS-001	requirements/srs/
Software Design Description	ALU-SDD-001	design/sdd/

Both documents follow the MIL-STD-498 DID structure and are rendered into the documentation site alongside the quickstart and tutorial.

Bug Tracker

Any feature requests or bug reports shall go to the todos of alusta.

Primary Source repository

The main source of alusta is on a mountain in Central Switzerland under configuration control (fossil).

Contributions

If you like to share small changes under the repositories license please kindly do so by sending a patchset. You can send such a patchset per email using git send-email.

Support

Please kindly submit issues at https://todo.sr.ht/~sthagen/alusta or write plain text email to ~sthagen/[e-mail] to support. Thanks.

Changes

See docs/changes.md for the release history.

Coverage

The test suite maintains 100% branch coverage. The HTML report (if generated) is in site/coverage/.

SBOM

Runtime dependency information is published in docs/sbom/ in SPDX 3.0 (JSON-LD) and CycloneDX 1.6 (JSON) formats. See docs/sbom/README.md for the component inventory and validation guide.