text: 'use strict'
  
  // tar -u
  
  const hlo = require('./high-level-opt.js')
  const r = require('./replace.js')
  // just call tar.r with the filter and mtimeCache
  
  const u = module.exports = (opt_, files, cb) => {
    const opt = hlo(opt_)
  
    if (!opt.file)
      throw new TypeError('file is required')
  
    if (opt.gzip)
      throw new TypeError('cannot append to compressed archives')
  
    if (!files || !Array.isArray(files) || !files.length)
      throw new TypeError('no files or directories specified')
  
    files = Array.from(files)
  
    mtimeFilter(opt)
    return r(opt, files, cb)
  }
  
  const mtimeFilter = opt => {
    const filter = opt.filter
  
    if (!opt.mtimeCache)
      opt.mtimeCache = new Map()
  
    opt.filter = filter ? (path, stat) =>
      filter(path, stat) && !(opt.mtimeCache.get(path) > stat.mtime)
      : (path, stat) => !(opt.mtimeCache.get(path) > stat.mtime)
  }
  