text: module.exports = which
  which.sync = whichSync
  
  var path = require("path")
    , fs
    , COLON = process.platform === "win32" ? ";" : ":"
    , isExe
    , 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 & 0010) && process.getuid && 0   === process.getuid()
          || (mod & 0100) && process.getuid && uid === process.getuid()
          || (mod & 0100) && process.getuid && 0   === 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 === ""
  }
  