This package parses [SPDX license expression](https://spdx.org/spdx-specification-21-web-version#h.jxpfx0ykyb60) strings describing license terms, like [package.json license strings](https://docs.npmjs.com/files/package.json#license), into consistently structured ECMAScript objects. The npm command-line interface depends on this package, as do many automatic license-audit tools. In a nutshell: ```javascript 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)](https://spdx.org/), a standard from the [Linux Foundation](https://www.linuxfoundation.org) 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](https://spdx.org/licenses), a mapping from specific string identifiers, like `Apache-2.0`, to standard form license texts and bolt-on license exceptions. The [spdx-license-ids](https://www.npmjs.com/package/spdx-license-ids) and [spdx-exceptions](https://www.npmjs.com/package/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: ```javascript 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: ```javascript 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. ```javascript 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")](http://spdx.org/licenses/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.