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parse SPDX license expressions


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This package parses SPDX license expression strings describing license terms, like package.json license strings, into consistently structured ECMAScript objects. The npm command-line interface depends on this package, as do many automatic license-audit tools.

In a nutshell:

var parse = require('spdx-expression-parse') var assert = require('assert') assert.deepEqual( // Licensed under the terms of the Two-Clause BSD License. parse('BSD-2-Clause'), {license: 'BSD-2-Clause'} ) assert.throws(function () { // An invalid SPDX license expression. // Should be `Apache-2.0`. parse('Apache 2') }) assert.deepEqual( // Dual licensed under either: // - LGPL 2.1 // - a combination of Three-Clause BSD and MIT parse('(LGPL-2.1 OR BSD-3-Clause AND MIT)'), { left: {license: 'LGPL-2.1'}, conjunction: 'or', right: { left: {license: 'BSD-3-Clause'}, conjunction: 'and', right: {license: 'MIT'} } } )

The syntax comes from the Software Package Data eXchange (SPDX), a standard from the Linux Foundation for shareable data about software package license terms. SPDX aims to make sharing and auditing license data easy, especially for users of open-source software.

The bulk of the SPDX standard describes syntax and semantics of XML metadata files. This package implements two lightweight, plain-text components of that larger standard:

  1. The license list, a mapping from specific string identifiers, like Apache-2.0, to standard form license texts and bolt-on license exceptions. The spdx-license-ids and spdx-exceptions packages implement the license list. spdx-expression-parse depends on and require()s them.

    Any license identifier from the license list is a valid license expression:

    var identifiers = [] .concat(require('spdx-license-ids')) .concat(require('spdx-license-ids/deprecated')) identifiers.forEach(function (id) { assert.deepEqual(parse(id), {license: id}) })

    So is any license identifier WITH a standardized license exception:

    identifiers.forEach(function (id) { require('spdx-exceptions').forEach(function (e) { assert.deepEqual( parse(id + ' WITH ' + e), {license: id, exception: e} ) }) })
  2. The license expression language, for describing simple and complex license terms, like MIT for MIT-licensed and (GPL-2.0 OR Apache-2.0) for dual-licensing under GPL 2.0 and Apache 2.0. spdx-expression-parse itself implements license expression language, exporting a parser.

    assert.deepEqual( // Licensed under a combination of: // - the MIT License AND // - a combination of: // - LGPL 2.1 (or a later version) AND // - Three-Clause BSD parse('(MIT AND (LGPL-2.1+ AND BSD-3-Clause))'), { left: {license: 'MIT'}, conjunction: 'and', right: { left: {license: 'LGPL-2.1', plus: true}, conjunction: 'and', right: {license: 'BSD-3-Clause'} } } )

The Linux Foundation and its contributors license the SPDX standard under the terms of the Creative Commons Attribution License 3.0 Unported (SPDX: "CC-BY-3.0"). "SPDX" is a United States federally registered trademark of the Linux Foundation. The authors of this package license their work under the terms of the MIT License.



Last updated on 13 May 2020

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