add hw2

node_modules/which/which.js

@@ -0,0 +1,125 @@
+const isWindows = process.platform === 'win32' ||
+    process.env.OSTYPE === 'cygwin' ||
+    process.env.OSTYPE === 'msys'
+
+const path = require('path')
+const COLON = isWindows ? ';' : ':'
+const isexe = require('isexe')
+
+const getNotFoundError = (cmd) =>
+  Object.assign(new Error(`not found: ${cmd}`), { code: 'ENOENT' })
+
+const getPathInfo = (cmd, opt) => {
+  const colon = opt.colon || COLON
+
+  // If it has a slash, then we don't bother searching the pathenv.
+  // just check the file itself, and that's it.
+  const pathEnv = cmd.match(/\//) || isWindows && cmd.match(/\\/) ? ['']
+    : (
+      [
+        // windows always checks the cwd first
+        ...(isWindows ? [process.cwd()] : []),
+        ...(opt.path || process.env.PATH ||
+          /* istanbul ignore next: very unusual */ '').split(colon),
+      ]
+    )
+  const pathExtExe = isWindows
+    ? opt.pathExt || process.env.PATHEXT || '.EXE;.CMD;.BAT;.COM'
+    : ''
+  const pathExt = isWindows ? pathExtExe.split(colon) : ['']
+
+  if (isWindows) {
+    if (cmd.indexOf('.') !== -1 && pathExt[0] !== '')
+      pathExt.unshift('')
+  }
+
+  return {
+    pathEnv,
+    pathExt,
+    pathExtExe,
+  }
+}
+
+const which = (cmd, opt, cb) => {
+  if (typeof opt === 'function') {
+    cb = opt
+    opt = {}
+  }
+  if (!opt)
+    opt = {}
+
+  const { pathEnv, pathExt, pathExtExe } = getPathInfo(cmd, opt)
+  const found = []
+
+  const step = i => new Promise((resolve, reject) => {
+    if (i === pathEnv.length)
+      return opt.all && found.length ? resolve(found)
+        : reject(getNotFoundError(cmd))
+
+    const ppRaw = pathEnv[i]
+    const pathPart = /^".*"$/.test(ppRaw) ? ppRaw.slice(1, -1) : ppRaw
+
+    const pCmd = path.join(pathPart, cmd)
+    const p = !pathPart && /^\.[\\\/]/.test(cmd) ? cmd.slice(0, 2) + pCmd
+      : pCmd
+
+    resolve(subStep(p, i, 0))
+  })
+
+  const subStep = (p, i, ii) => new Promise((resolve, reject) => {
+    if (ii === pathExt.length)
+      return resolve(step(i + 1))
+    const ext = pathExt[ii]
+    isexe(p + ext, { pathExt: pathExtExe }, (er, is) => {
+      if (!er && is) {
+        if (opt.all)
+          found.push(p + ext)
+        else
+          return resolve(p + ext)
+      }
+      return resolve(subStep(p, i, ii + 1))
+    })
+  })
+
+  return cb ? step(0).then(res => cb(null, res), cb) : step(0)
+}
+
+const whichSync = (cmd, opt) => {
+  opt = opt || {}
+
+  const { pathEnv, pathExt, pathExtExe } = getPathInfo(cmd, opt)
+  const found = []
+
+  for (let i = 0; i < pathEnv.length; i ++) {
+    const ppRaw = pathEnv[i]
+    const pathPart = /^".*"$/.test(ppRaw) ? ppRaw.slice(1, -1) : ppRaw
+
+    const pCmd = path.join(pathPart, cmd)
+    const p = !pathPart && /^\.[\\\/]/.test(cmd) ? cmd.slice(0, 2) + pCmd
+      : pCmd
+
+    for (let j = 0; j < pathExt.length; j ++) {
+      const cur = p + pathExt[j]
+      try {
+        const is = isexe.sync(cur, { pathExt: pathExtExe })
+        if (is) {
+          if (opt.all)
+            found.push(cur)
+          else
+            return cur
+        }
+      } catch (ex) {}
+    }
+  }
+
+  if (opt.all && found.length)
+    return found
+
+  if (opt.nothrow)
+    return null
+
+  throw getNotFoundError(cmd)
+}
+
+module.exports = which
+which.sync = whichSync