_

$ tar cvf x.tar package
a package
a package/.gitignore

$ node rename.js
entry package/
extracting package/
entry package/.gitignore
renaming package/.gitignore to package/.npmignore
extracting package/.npmignore

$ tree output/
output/
└── .npmignore

0 directories, 1 file

rename.js

'use strict'
const tar = require('./')
const file = 'x.tar'
const mkdirp = require('mkdirp')
const path = require('path')
const rimraf = require('rimraf')

rimraf.sync('output')
mkdirp.sync('output')

const sawIgnores = new Set()

tar.x({
  file: file,
  cwd: 'output',
  strip: 1,
  onentry: entry => {
    console.error('entry', entry.path)
    // Note: This mirrors logic in the fs read operations that are
    // employed during tarball creation, in the fstream-npm module.
    // It is duplicated here to handle tarballs that are created
    // using other means, such as system tar or git archive.
    if (entry.type.toLowerCase() === 'file') {
      const base = path.basename(entry.path)
      if (base === '.npmignore') {
        sawIgnores.add(entry.path)
      } else if (base === '.gitignore') {
        const npmignore = entry.path.replace(/\.gitignore$/, '.npmignore')
        if (!sawIgnores.has(npmignore)) {
          // Rename, may be clobbered later.
          console.log('renaming', entry.path, 'to', npmignore)
          entry.path = npmignore
        }
      }
    }

    console.log('extracting', entry.path)
  }
})