function fmtIec(n, si) {
  const base = si ? 1000 : 1024
  const units = si
    ? ['', 'k', 'M', 'G', 'T', 'P']
    : ['', 'K', 'M', 'G', 'T', 'P']
  if (n === 0) return '0'
  let sign = n < 0 ? -1 : 1
  let x = Math.abs(n)
  let u = 0
  while (x >= base && u < units.length - 1) {
    x /= base
    u++
  }
  const s =
    x >= 10 || u === 0 ? Math.round(x * 10) / 10 : Math.round(x * 100) / 100
  const t = String(s).replace(/\.0$/, '')
  return (sign < 0 ? '-' : '') + t + units[u]
}

async function run(ctx, argv) {
  let toIec = false
  let toSi = false
  const rest = []
  for (let i = 1; i < argv.length; i++) {
    const a = argv[i]
    if (a === '-h' || a === '--help') {
      ctx.console.log(
        'usage: numfmt [--to=iec|--to=si] [NUMBER]...\nFormat numbers; reads stdin lines if no operands.'
      )
      return
    }
    if (a === '--to=iec') toIec = true
    else if (a === '--to=si') toSi = true
    else if (a.startsWith('-')) {
      ctx.console.error('numfmt: unsupported option ' + a)
      ctx.exitCode = 1
      return
    } else rest.push(a)
  }
  if (!toIec && !toSi) toIec = true
  const nums = []
  if (!rest.length) {
    for (const line of bareStdin(ctx).split('\n')) {
      const t = line.trim()
      if (!t) continue
      nums.push(t)
    }
  } else nums.push(...rest)
  for (const s of nums) {
    const n = parseInt(s, 10)
    if (!Number.isFinite(n)) {
      ctx.console.error('numfmt: invalid number ' + s)
      ctx.exitCode = 1
      return
    }
    ctx.console.log(fmtIec(n, toSi))
  }
}