node/deps/npm/node_modules/which/which.js

module.exports = which
which.sync = whichSync

var path = require("path")
  , fs
  , COLON = process.platform === "win32" ? ";" : ":"
  , isExe

try {
  fs = require("graceful-fs")
} catch (ex) {
  fs = require("fs")
}

if (process.platform == "win32") {
  // On windows, there is no good way to check that a file is executable
  isExe = function isExe () { return true }
} else {
  isExe = function isExe (mod, uid, gid) {
    //console.error(mod, uid, gid);
    //console.error("isExe?", (mod & 0111).toString(8))
    var ret = (mod & 0001)
        || (mod & 0010) && process.getgid && gid === process.getgid()
        || (mod & 0100) && process.getuid && uid === process.getuid()
    //console.error("isExe?", ret)
    return ret
  }
}



function which (cmd, cb) {
  if (isAbsolute(cmd)) return cb(null, cmd)
  var pathEnv = (process.env.PATH || "").split(COLON)
    , pathExt = [""]
  if (process.platform === "win32") {
    pathEnv.push(process.cwd())
    pathExt = (process.env.PATHEXT || ".EXE").split(COLON)
    if (cmd.indexOf(".") !== -1) pathExt.unshift("")
  }
  //console.error("pathEnv", pathEnv)
  ;(function F (i, l) {
    if (i === l) return cb(new Error("not found: "+cmd))
    var p = path.resolve(pathEnv[i], cmd)
    ;(function E (ii, ll) {
      if (ii === ll) return F(i + 1, l)
      var ext = pathExt[ii]
      //console.error(p + ext)
      fs.stat(p + ext, function (er, stat) {
        if (!er &&
            stat &&
            stat.isFile() &&
            isExe(stat.mode, stat.uid, stat.gid)) {
          //console.error("yes, exe!", p + ext)
          return cb(null, p + ext)
        }
        return E(ii + 1, ll)
      })
    })(0, pathExt.length)
  })(0, pathEnv.length)
}

function whichSync (cmd) {
  if (isAbsolute(cmd)) return cmd
  var pathEnv = (process.env.PATH || "").split(COLON)
    , pathExt = [""]
  if (process.platform === "win32") {
    pathEnv.push(process.cwd())
    pathExt = (process.env.PATHEXT || ".EXE").split(COLON)
    if (cmd.indexOf(".") !== -1) pathExt.unshift("")
  }
  for (var i = 0, l = pathEnv.length; i < l; i ++) {
    var p = path.join(pathEnv[i], cmd)
    for (var j = 0, ll = pathExt.length; j < ll; j ++) {
      var cur = p + pathExt[j]
      var stat
      try { stat = fs.statSync(cur) } catch (ex) {}
      if (stat &&
          stat.isFile() &&
          isExe(stat.mode, stat.uid, stat.gid)) return cur
    }
  }
  throw new Error("not found: "+cmd)
}

var isAbsolute = process.platform === "win32" ? absWin : absUnix

function absWin (p) {
  if (absUnix(p)) return true
  // pull off the device/UNC bit from a windows path.
  // from node's lib/path.js
  var splitDeviceRe =
        /^([a-zA-Z]:|[\\\/]{2}[^\\\/]+[\\\/][^\\\/]+)?([\\\/])?/
    , result = splitDeviceRe.exec(p)
    , device = result[1] || ''
    , isUnc = device && device.charAt(1) !== ':'
    , isAbsolute = !!result[2] || isUnc // UNC paths are always absolute

  return isAbsolute
}

function absUnix (p) {
  return p.charAt(0) === "/" || p === ""
}