om/node_modules/mv/index.js

var fs = require('fs');
var ncp = require('ncp').ncp;
var path = require('path');
var rimraf = require('rimraf');
var mkdirp = require('mkdirp');

module.exports = mv;

function mv(source, dest, options, cb){
  if (typeof options === 'function') {
    cb = options;
    options = {};
  }
  var shouldMkdirp = !!options.mkdirp;
  var clobber = options.clobber !== false;
  var limit = options.limit || 16;

  if (shouldMkdirp) {
    mkdirs();
  } else {
    doRename();
  }

  function mkdirs() {
    mkdirp(path.dirname(dest), function(err) {
      if (err) return cb(err);
      doRename();
    });
  }

  function doRename() {
    if (clobber) {
      fs.rename(source, dest, function(err) {
        if (!err) return cb();
        if (err.code !== 'EXDEV') return cb(err);
        moveFileAcrossDevice(source, dest, clobber, limit, cb);
      });
    } else {
      fs.link(source, dest, function(err) {
        if (err) {
          if (err.code === 'EXDEV') {
            moveFileAcrossDevice(source, dest, clobber, limit, cb);
            return;
          }
          if (err.code === 'EISDIR' || err.code === 'EPERM') {
            moveDirAcrossDevice(source, dest, clobber, limit, cb);
            return;
          }
          cb(err);
          return;
        }
        fs.unlink(source, cb);
      });
    }
  }
}

function moveFileAcrossDevice(source, dest, clobber, limit, cb) {
  var outFlags = clobber ? 'w' : 'wx';
  var ins = fs.createReadStream(source);
  var outs = fs.createWriteStream(dest, {flags: outFlags});
  ins.on('error', function(err){
    ins.destroy();
    outs.destroy();
    outs.removeListener('close', onClose);
    if (err.code === 'EISDIR' || err.code === 'EPERM') {
      moveDirAcrossDevice(source, dest, clobber, limit, cb);
    } else {
      cb(err);
    }
  });
  outs.on('error', function(err){
    ins.destroy();
    outs.destroy();
    outs.removeListener('close', onClose);
    cb(err);
  });
  outs.once('close', onClose);
  ins.pipe(outs);
  function onClose(){
    fs.unlink(source, cb);
  }
}

function moveDirAcrossDevice(source, dest, clobber, limit, cb) {
  var options = {
    stopOnErr: true,
    clobber: false,
    limit: limit,
  };
  if (clobber) {
    rimraf(dest, { disableGlob: true }, function(err) {
      if (err) return cb(err);
      startNcp();
    });
  } else {
    startNcp();
  }
  function startNcp() {
    ncp(source, dest, options, function(errList) {
      if (errList) return cb(errList[0]);
      rimraf(source, { disableGlob: true }, cb);
    });
  }
}