Check synchronously if file/directory exists in No

问题:

How can I synchronously check, using node.js, if a file or directory exists?

回答1:

The answer to this question has changed over the years. The current answer is here at the top, followed by the various answers over the years in chronological order:

Current Answer

You can use fs.existsSync():

var fs = require(\'fs\');
if (fs.existsSync(path)) {
    // Do something
}

It was deprecated for several years, but no longer is. From the docs:

Note that fs.exists() is deprecated, but fs.existsSync() is not. (The callback parameter to fs.exists() accepts parameters that are inconsistent with other Node.js callbacks. fs.existsSync() does not use a callback.)

You\'ve specifically asked for a synchronous check, but if you can use an asynchronous check instead (usually best with I/O), use fs.access (since exists is deprecated).

---

Historical Answers

Here are the historical answers in chronological order:

• Original answer from 2010
  (stat/statSync or lstat/lstatSync)
• Update September 2012
  (exists/existsSync)
• Update February 2015
  (Noting impending deprecation of exists/existsSync, so we\'re probably back to stat/statSync or lstat/lstatSync)
• Update December 2015
  (There\'s also fs.access(path, fs.F_OK, function(){}) / fs.accessSync(path, fs.F_OK), but note that if the file/directory doesn\'t exist, it\'s an error; docs for fs.stat recommend using fs.access if you need to check for existence without opening)
• Update December 2016
  fs.exists() is still deprecated but fs.existsSync() is no longer deprecated. So you can safely use it now.

Original answer from 2010:

You can use statSync or lstatSync (docs link), which give you an fs.Stats object. In general, if a synchronous version of a function is available, it will have the same name as the async version with Sync at the end. So statSync is the synchronous version of stat; lstatSync is the synchronous version of lstat, etc.

lstatSync tells you both whether something exists, and if so, whether it\'s a file or a directory (or in some file systems, a symbolic link, block device, character device, etc.), e.g. if you need to know if it exists and is a directory:

var fs = require(\'fs\');
try {
    // Query the entry
    stats = fs.lstatSync(\'/the/path\');

    // Is it a directory?
    if (stats.isDirectory()) {
        // Yes it is
    }
}
catch (e) {
    // ...
}

...and similarly if it\'s a file, there\'s isFile; if it\'s a block device, there\'s isBlockDevice, etc., etc. Note the try/catch; it throws an error if the entry doesn\'t exist at all.

If you don\'t care what the entry is and only want to know whether it exists, you can use path.existsSync (or with latest, fs.existsSync) as noted by user618408:

var path = require(\'path\');
if (path.existsSync(\"/the/path\")) { // or fs.existsSync
    // ...
}

It doesn\'t require a try/catch, but gives you no information about what the thing is, just that it\'s there. path.existsSync was deprecated long ago.

---

Side note: You\'ve expressly asked how to check synchronously, so I\'ve used the xyzSync versions of the functions above. But wherever possible, with I/O, it really is best to avoid synchronous calls. Calls into the I/O subsystem take significant time from a CPU\'s point of view. Note how easy it is to call lstat rather than lstatSync:

// Is it a directory?
lstat(\'/the/path\', function(err, stats) {
    if (!err && stats.isDirectory()) {
        // Yes it is
    }
});

But if you need the synchronous version, it\'s there.

Update September 2012

The below answer from a couple of years ago is now a bit out of date. The current way is to use fs.existsSync to do a synchronous check for file/directory existence (or of course fs.exists for an asynchronous check), rather than the path versions below.

Example:

var fs = require(\'fs\');

if (fs.existsSync(path)) {
    // Do something
}

// Or

fs.exists(path, function(exists) {
    if (exists) {
        // Do something
    }
});

Update February 2015

And here we are in 2015 and the Node docs now say that fs.existsSync (and fs.exists) \"will be deprecated\". (Because the Node folks think it\'s dumb to check whether something exists before opening it, which it is; but that\'s not the only reason for checking whether something exists!)

So we\'re probably back to the various stat methods... Until/unless this changes yet again, of course.

Update December 2015

Don\'t know how long it\'s been there, but there\'s also fs.access(path, fs.F_OK, ...) / fs.accessSync(path, fs.F_OK). And at least as of October 2016, the fs.stat documentation recommends using fs.access to do existence checks (\"To check if a file exists without manipulating it afterwards, fs.access() is recommended.\"). But note that the access not being available is considered an error, so this would probably be best if you\'re expecting the file to be accessible:

var fs = require(\'fs\');

try {
    fs.accessSync(path, fs.F_OK);
    // Do something
} catch (e) {
    // It isn\'t accessible
}

// Or

fs.access(path, fs.F_OK, function(err) {
    if (!err) {
        // Do something
    } else {
        // It isn\'t accessible
    }
});

Update December 2016

You can use fs.existsSync():

if (fs.existsSync(path)) {
    // Do something
}

It was deprecated for several years, but no longer is. From the docs:

Note that fs.exists() is deprecated, but fs.existsSync() is not. (The callback parameter to fs.exists() accepts parameters that are inconsistent with other Node.js callbacks. fs.existsSync() does not use a callback.)

回答2:

Looking at the source, there\'s a synchronous version of path.exists - path.existsSync. Looks like it got missed in the docs.

Update:

path.exists and path.existsSync are now deprecated. Please use fs.exists and fs.existsSync.

Update 2016:

fs.exists and fs.existsSync have also been deprecated. Use fs.stat() or fs.access() instead.

回答3:

Using the currently recommended (as of 2015) APIs (per the Node docs), this is what I do:

var fs = require(\'fs\');

function fileExists(filePath)
{
    try
    {
        return fs.statSync(filePath).isFile();
    }
    catch (err)
    {
        return false;
    }
}

In response to the EPERM issue raised by @broadband in the comments, that brings up a good point. fileExists() is probably not a good way to think about this in many cases, because fileExists() can\'t really promise a boolean return. You may be able to determine definitively that the file exists or doesn\'t exist, but you may also get a permissions error. The permissions error doesn\'t necessarily imply that the file exists, because you could lack permission to the directory containing the file on which you are checking. And of course there is the chance you could encounter some other error in checking for file existence.

So my code above is really doesFileExistAndDoIHaveAccessToIt(), but your question might be doesFileNotExistAndCouldICreateIt(), which would be completely different logic (that would need to account for an EPERM error, among other things).

While the fs.existsSync answer addresses the question asked here directly, that is often not going to be what you want (you don\'t just want to know if \"something\" exists at a path, you probably care about whether the \"thing\" that exists is a file or a directory).

The bottom line is that if you\'re checking to see if a file exists, you are probably doing that because you intend to take some action based on the result, and that logic (the check and/or subsequent action) should accommodate the idea that a thing found at that path may be a file or a directory, and that you may encounter EPERM or other errors in the process of checking.

回答4:

Another Update

Needing an answer to this question myself I looked up the node docs, seems you should not be using fs.exists, instead use fs.open and use outputted error to detect if a file does not exist:

from the docs:

fs.exists() is an anachronism and exists only for historical reasons. There should almost never be a reason to use it in your own code.

In particular, checking if a file exists before opening it is an anti-pattern that leaves you vulnerable to race conditions: another process may remove the file between the calls to fs.exists() and fs.open(). Just open the file and handle the error when it\'s not there.

http://nodejs.org/api/fs.html#fs_fs_exists_path_callback

回答5:

I use below function to test if file exists. It catches also other exceptions. So in case there are rights issues e.g. chmod ugo-rwx filename or in Windows Right Click -> Properties -> Security -> Advanced -> Permission entries: empty list .. function returns exception as it should. The file exists but we don\'t have rights to access it. It would be wrong to ignore this kinds of exceptions.

function fileExists(path) {

  try  {
    return fs.statSync(path).isFile();
  }
  catch (e) {

    if (e.code == \'ENOENT\') { // no such file or directory. File really does not exist
      console.log(\"File does not exist.\");
      return false;
    }

    console.log(\"Exception fs.statSync (\" + path + \"): \" + e);
    throw e; // something else went wrong, we don\'t have rights, ...
  }
}

Exception output, nodejs errors documentation in case file doesn\'t exist:

{
  [Error: ENOENT: no such file or directory, stat \'X:\\\\delsdfsdf.txt\']
  errno: -4058,
  code: \'ENOENT\',
  syscall: \'stat\',
  path: \'X:\\\\delsdfsdf.txt\'
}

Exception in case we don\'t have rights to the file, but exists:

{
  [Error: EPERM: operation not permitted, stat \'X:\\file.txt\']
  errno: -4048,
  code: \'EPERM\',
  syscall: \'stat\',
  path: \'X:\\\\file.txt\'
}

回答6:

fs.exists() is deprecated dont use it https://nodejs.org/api/fs.html#fs_fs_exists_path_callback

You could implement the core nodejs way used at this: https://github.com/nodejs/node-v0.x-archive/blob/master/lib/module.js#L86

function statPath(path) {
  try {
    return fs.statSync(path);
  } catch (ex) {}
  return false;
}

this will return the stats object then once you\'ve got the stats object you could try

var exist = statPath(\'/path/to/your/file.js\');
if(exist && exist.isFile()) {
  // do something
}

回答7:

Some answers here says that fs.exists and fs.existsSync are both deprecated. According to the docs this is no more true. Only fs.exists is deprected now:

Note that fs.exists() is deprecated, but fs.existsSync() is not. (The callback parameter to fs.exists() accepts parameters that are inconsistent with other Node.js callbacks. fs.existsSync() does not use a callback.)

So you can safely use fs.existsSync() to synchronously check if a file exists.

回答8:

The path module does not provide a synchronous version of path.exists so you have to trick around with the fs module.

Fastest thing I can imagine is using fs.realpathSync which will throw an error that you have to catch, so you need to make your own wrapper function with a try/catch.

回答9:

Using fileSystem (fs) tests will trigger error objects, which you then would need to wrap in a try/catch statement. Save yourself some effort, and use a feature introduce in the 0.4.x branch.

var path = require(\'path\');

var dirs = [\'one\', \'two\', \'three\'];

dirs.map(function(dir) {
  path.exists(dir, function(exists) {
    var message = (exists) ? dir + \': is a directory\' : dir + \': is not a directory\';
    console.log(message);
  });
});

回答10:

The documents on fs.stat() says to use fs.access() if you are not going to manipulate the file. It did not give a justification, might be faster or less memeory use?

I use node for linear automation, so I thought I share the function I use to test for file existence.

var fs = require(\"fs\");

function exists(path){
    //Remember file access time will slow your program.
    try{
        fs.accessSync(path);
    } catch (err){
        return false;
    }
    return true;
}

回答11:

Here is a simple wrapper solution for this:

var fs = require(\'fs\')
function getFileRealPath(s){
    try {return fs.realpathSync(s);} catch(e){return false;}
}

Usage:

• Works for both directories and files
• If item exists, it returns the path to the file or directory
• If item does not exist, it returns false

Example:

var realPath,pathToCheck=\'<your_dir_or_file>\'
if( (realPath=getFileRealPath(pathToCheck)) === false){
    console.log(\'file/dir not found: \'+pathToCheck);
} else {
    console.log(\'file/dir exists: \'+realPath);
}

Make sure you use === operator to test if return equals false. There is no logical reason that fs.realpathSync() would return false under proper working conditions so I think this should work 100%.

I would prefer to see a solution that does not does not generate an Error and resulting performance hit. From an API perspective, fs.exists() seems like the most elegant solution.

回答12:

Async Promise solution (bluebirdjs)

For those using bluebirdjs and nodejs 7. The best way to return a boolean promise:

function fileExists(path){
  return fs.accessAsync(path, fs.constants.F_OK) //F_OK checks if file is visible, is default does no need to be specified.
         .then(err => !err);
}

the docs: https://nodejs.org/api/fs.html#fs_fs_access_path_mode_callback

回答13:

From the answers it appears that there is no official API support for this (as in a direct and explicit check). Many of the answers say to use stat, however they are not strict. We can\'t assume for example that any error thrown by stat means that something doesn\'t exist.

Lets say we try it with something that doesn\'t exist:

$ node -e \'require(\"fs\").stat(\"god\",err=>console.log(err))\'
{ Error: ENOENT: no such file or directory, stat \'god\' errno: -2, code: \'ENOENT\', syscall: \'stat\', path: \'god\' }

Lets try it with something that exists but that we don\'t have access to:

$ mkdir -p fsm/appendage && sudo chmod 0 fsm
$ node -e \'require(\"fs\").stat(\"fsm/appendage\",err=>console.log(err))\'
{ Error: EACCES: permission denied, stat \'access/access\' errno: -13, code: \'EACCES\', syscall: \'stat\', path: \'fsm/appendage\' }

At the very least you\'ll want:

let dir_exists = async path => {
    let stat;
    try {
       stat = await (new Promise(
           (resolve, reject) => require(\'fs\').stat(path,
               (err, result) => err ? reject(err) : resolve(result))
       ));
    }
    catch(e) {
        if(e.code === \'ENOENT\') return false;
        throw e;
    }

    if(!stat.isDirectory())
        throw new Error(\'Not a directory.\');

    return true;
};

The question question is not clear on if you actually want it to be syncronous or if you only want it to be written as though it is syncronous. This example uses await/async so that it is only written syncronously but runs asyncronously.

This means you have to call it as such at the top level:

(async () => {
    try {
        console.log(await dir_exists(\'god\'));
        console.log(await dir_exists(\'fsm/appendage\'));
    }
    catch(e) {
        console.log(e);
    }
})();

An alternative is using .then and .catch on the promise returned from the async call if you need it further down.

If you want to check if something exists then it\'s a good practice to also ensure it\'s the right type of thing such as a directory or file. This is included in the example. If it\'s not allowed to be a symlink you must use lstat instead of stat as stat will automatically traverse links.

You can replace all of the async to sync code in here and use statSync instead. However expect that once async and await become universally supports the Sync calls will become redundant eventually to be depreciated (otherwise you would have to define them everywhere and up the chain just like with async making it really pointless).