node.js中的fs.realpathSync方法使用说明

方法说明：

同步版的 fs.realpath() 。

语法：

fs.realpathSync(path, [cache])

由于该方法属于fs模块，使用前需要引入fs模块（var fs= require(“fs”) ）

接收参数：

path 路径

cache 可选，一个文字的映射路径可用于强制一个特定的路径解决或避免额外的fs.stat需要知道真正的路径对象。

例子：

var fs = require('fs');

// 点号表示当前文件所在路径

var str = fs.realpathSync('.');

console.log(str);

源码：

fs.realpathSync = function realpathSync(p, cache) {

  // make p is absolute

  p = pathModule.resolve(p);

  if (cache && Object.prototype.hasOwnProperty.call(cache, p)) {

    return cache[p];

  }

  var original = p,

      seenLinks = {},

      knownHard = {};

  // current character position in p

  var pos;

  // the partial path so far, including a trailing slash if any

  var current;

  // the partial path without a trailing slash (except when pointing at a root)

  var base;

  // the partial path scanned in the previous round, with slash

  var previous;

  start();

  function start() {

    // Skip over roots

    var m = splitRootRe.exec(p);

    pos = m[0].length;

    current = m[0];

    base = m[0];

    previous = '';

    // On windows, check that the root exists. On unix there is no need.

    if (isWindows && !knownHard[base]) {

      fs.lstatSync(base);

      knownHard[base] = true;

    }

  }

  // walk down the path, swapping out linked pathparts for their real

  // values

  // NB: p.length changes.

  while (pos < p.length) {

    // find the next part

    nextPartRe.lastIndex = pos;

    var result = nextPartRe.exec(p);

    previous = current;

    current += result[0];

    base = previous + result[1];

    pos = nextPartRe.lastIndex;

    // continue if not a symlink

    if (knownHard[base] || (cache && cache[base] === base)) {

      continue;

    }

    var resolvedLink;

    if (cache && Object.prototype.hasOwnProperty.call(cache, base)) {

      // some known symbolic link. no need to stat again.

      resolvedLink = cache[base];

    } else {

      var stat = fs.lstatSync(base);

      if (!stat.isSymbolicLink()) {

        knownHard[base] = true;

        if (cache) cache[base] = base;

        continue;

      }

      // read the link if it wasn't read before

      // dev/ino always return 0 on windows, so skip the check.

      var linkTarget = null;

      if (!isWindows) {

        var id = stat.dev.toString(32) + ':' + stat.ino.toString(32);

        if (seenLinks.hasOwnProperty(id)) {

          linkTarget = seenLinks[id];

        }

      }

      if (util.isNull(linkTarget)) {

        fs.statSync(base);

        linkTarget = fs.readlinkSync(base);

      }

      resolvedLink = pathModule.resolve(previous, linkTarget);

      // track this, if given a cache.

      if (cache) cache[base] = resolvedLink;

      if (!isWindows) seenLinks[id] = linkTarget;

    }

    // resolve the link, then start over

    p = pathModule.resolve(resolvedLink, p.slice(pos));

    start();

  }

  if (cache) cache[original] = p;

  return p;

};