npm install -g sfdc-merge-package

yarn globally add sfdc-merge-package

$ smp -h

  Usage: smp [options]

  Merge package.xml

  Options:

    -h, --help                   output usage information
    -V, --version                output the version number
    -p, --packages               path to the packages.xml
    -o, --output                 path where to output the merged package.xml

  var smp = require('sfdc-merge-package');

  smp({
    'packages':'./src/packages.xml' // path to the packages.xml
  }, console.log);