> For the complete documentation index, see [llms.txt](https://bryan-guner.gitbook.io/my-docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://bryan-guner.gitbook.io/my-docs/redux/repos/examples/real-world/node_modules/spdx-expression-parse.md).

# spdx-expression-parse

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.