docs: function library(argv, config, args) {
    if (!isValidPackageName(args.name)) {
      return Promise.reject(
        args.name + ' is not a valid name for a project. Please use a valid ' +
        'identifier name (alphanumeric).'
      );
    }
  
    const root = process.cwd();
    const libraries = path.resolve(root, 'Libraries');
    const libraryDest = path.resolve(libraries, args.name);
    const source = path.resolve('node_modules', 'react-native', 'Libraries', 'Sample');
  
    if (!fs.existsSync(libraries)) {
      fs.mkdir(libraries);
    }
  
    if (fs.existsSync(libraryDest)) {
      return Promise.reject(`Library already exists in ${libraryDest}`);
    }
  
    walk(source).forEach(f => {
      if (f.indexOf('project.xcworkspace') !== -1 ||
          f.indexOf('.xcodeproj/xcuserdata') !== -1) {
        return;
      }
  
      const dest = f.replace(/Sample/g, args.name).replace(/^_/, '.');
      copyAndReplace(
        path.resolve(source, f),
        path.resolve(libraryDest, dest),
        {'Sample': args.name}
      );
    });
  
    console.log('Created library in', libraryDest);
    console.log('Next Steps:');
    console.log('   Link your library in Xcode:');
    console.log(
      '   https://facebook.github.io/react-native/docs/' +
      'linking-libraries-ios.html#content\n'
    );
  }