README

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:

   ```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"). "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.