Programs & Examples On #Node.js

Node.js is an event-based, non-blocking, asynchronous I/O framework that uses Google's V8 JavaScript engine and libuv library. It is used for developing applications that make heavy use of the ability to run JavaScript both on the client, as well as on server side and therefore benefit from the re-usability of code and the lack of context switching.

Reading value from console, interactively

I recommend using Inquirer, since it provides a collection of common interactive command line user interfaces.

const inquirer = require('inquirer');

const questions = [{
  type: 'input',
  name: 'name',
  message: "What's your name?",

const answers = await inquirer.prompt(questions);

How do I get the domain originating the request in express.js?

In Express 4.x you can use req.hostname, which returns the domain name, without port. i.e.:

// Host: ""
// => ""


How to downgrade Node version

For windows 10,

  • Uninstalling the node from the "Add or remove programs"
  • Installing the required version from

worked for me.

How to programmatically send a 404 response with Express/Node?

From the Express site, define a NotFound exception and throw it whenever you want to have a 404 page OR redirect to /404 in the below case:

function NotFound(msg){ = 'NotFound';, msg);
  Error.captureStackTrace(this, arguments.callee);

NotFound.prototype.__proto__ = Error.prototype;

app.get('/404', function(req, res){
  throw new NotFound;

app.get('/500', function(req, res){
  throw new Error('keyboard cat!');

Mongoose: Find, modify, save

If you want to use find, like I would for any validation you want to do on the client side.

find returns an ARRAY of objects

findOne returns only an object

Adding user = user[0] made the save method work for me.

Here is where you put it.

User.find({username: oldUsername}, function (err, user) {
    user = user[0];
    user.username = newUser.username;
    user.password = newUser.password;
    user.rights = newUser.rights; (err) {
        if(err) {

pass JSON to HTTP POST Request

I worked on this for too long. The answer that helped me was at: send Content-Type: application/json post with node.js

Which uses the following format:

    url: url,
    method: "POST",
    headers: {
        "content-type": "application/json",
    json: requestData
//  body: JSON.stringify(requestData)
    }, function (error, resp, body) { ...

List of encodings that Node.js supports

The encodings are spelled out in the buffer documentation.

Buffers and character encodings:

Character Encodings

  • utf8: Multi-byte encoded Unicode characters. Many web pages and other document formats use UTF-8. This is the default character encoding.
  • utf16le: Multi-byte encoded Unicode characters. Unlike utf8, each character in the string will be encoded using either 2 or 4 bytes.
  • latin1: Latin-1 stands for ISO-8859-1. This character encoding only supports the Unicode characters from U+0000 to U+00FF.

Binary-to-Text Encodings

  • base64: Base64 encoding. When creating a Buffer from a string, this encoding will also correctly accept "URL and Filename Safe Alphabet" as specified in RFC 4648, Section 5.
  • hex: Encode each byte as two hexadecimal characters.

Legacy Character Encodings

  • ascii: For 7-bit ASCII data only. Generally, there should be no reason to use this encoding, as 'utf8' (or, if the data is known to always be ASCII-only, 'latin1') will be a better choice when encoding or decoding ASCII-only text.
  • binary: Alias for 'latin1'.
  • ucs2: Alias of 'utf16le'.

Calling a JSON API with Node.js

Another solution is to user axios:

npm install axios

Code will be like:

const url = `${this.env.someMicroservice.address}/v1/my-end-point`;

const { data } = await axios.get<MyInterface>(url, {
  auth: {
    username: this.env.auth.user,
    password: this.env.auth.pass

return data;

Sending emails in Node.js?

Mature, simple to use and has lots of features if simple isn't enought: Nodemailer: (note correct url!)

Node Version Manager (NVM) on Windows

NVM Installation & usage on Windows

Below are the steps for NVM Installation on Windows:

NVM stands for node version manager, which will help to switch between node versions while also allowing to work with multiple npm versions.

  • Install nvm setup.
  • Use command nvm list to check list of installed node versions.
  • Example: Type nvm use 6.9.3 to switch versions.

For more info

Mongoose.js: Find user by username LIKE value

    username: /peter/i
}, function (err, user) {

How Do I Uninstall Yarn

npm uninstall yarn removes the yarn packages that are installed via npm but what yarn does underneath the hood is, it installs a software named yarn in your PC. If you have installed in Windows, Go to add or remove programs and then search for yarn and uninstall it then you are good to go.

Good beginners tutorial to

To start with Socket.IO I suggest you read first the example on the main page:

On the server side, read the "How to use" on the GitHub source page:

And on the client side:

Finally you need to read this great tutorial:

Hint: At the end of this blog post, you will have some links pointing on source code that could be some help.

How to make a function wait until a callback has been called using node.js

supposing you have a function:

var fetchPage(page, callback) {
   request(uri, function (error, response, body) {
        if (something_good) {
          callback(true, page+1);
        } else {


you can make use of callbacks like this:

fetchPage(1, x = function(next, page) {
if (next) {
    console.log("^^^ CALLBACK -->  fetchPage: " + page);
    fetchPage(page, x);

Const in JavaScript: when to use it and is it necessary?

2017 Update

This answer still receives a lot of attention. It's worth noting that this answer was posted back at the beginning of 2014 and a lot has changed since then. support is now the norm. All modern browsers now support const so it should be pretty safe to use without any problems.

Original Answer from 2014

Despite having fairly decent browser support, I'd avoid using it for now. From MDN's article on const:

The current implementation of const is a Mozilla-specific extension and is not part of ECMAScript 5. It is supported in Firefox & Chrome (V8). As of Safari 5.1.7 and Opera 12.00, if you define a variable with const in these browsers, you can still change its value later. It is not supported in Internet Explorer 6-10, but is included in Internet Explorer 11. The const keyword currently declares the constant in the function scope (like variables declared with var).

It then goes on to say:

const is going to be defined by ECMAScript 6, but with different semantics. Similar to variables declared with the let statement, constants declared with const will be block-scoped.

If you do use const you're going to have to add in a workaround to support slightly older browsers.

Running Node.Js on Android

J2V8 is best solution of your problem. It's run Nodejs application on jvm(java and android).

J2V8 is Java Bindings for V8, But Node.js integration is available in J2V8 (version 4.4.0)

Github :

Example :

Reading all files in a directory, store them in objects, and send the object

Another version with Promise's modern method. It's shorter that the others responses based on Promise :

const readFiles = (dirname) => {

  const readDirPr = new Promise( (resolve, reject) => {
      (err, filenames) => (err) ? reject(err) : resolve(filenames))

  return readDirPr.then( filenames => Promise.all( => {
      return new Promise ( (resolve, reject) => {
        fs.readFile(dirname + filename, 'utf-8',
          (err, content) => (err) ? reject(err) : resolve(content));
    })).catch( error => Promise.reject(error)))

  .then( allContents => {

    // handle success treatment

  }, error => console.log(error));

MongoError: connect ECONNREFUSED

Please ensure that your mongo DB is set Automatic and running at Control Panel/Administrative Tools/Services like below. That way you wont have to start mongod.exe manually each time.

enter image description here

What is Node.js?

Q: The programming model is event driven, especially the way it handles I/O.

Correct. It uses call-backs, so any request to access the file system would cause a request to be sent to the file system and then Node.js would start processing its next request. It would only worry about the I/O request once it gets a response back from the file system, at which time it will run the callback code. However, it is possible to make synchronous I/O requests (that is, blocking requests). It is up to the developer to choose between asynchronous (callbacks) or synchronous (waiting).

Q: It uses JavaScript and the parser is V8.


Q: It can be easily used to create concurrent server applications.

Yes, although you'd need to hand-code quite a lot of JavaScript. It might be better to look at a framework, such as - which comes with full online documentation and a sample application.

How to add /usr/local/bin in $PATH on Mac

Try placing $PATH at the end.

export PATH=/usr/local/git/bin:/usr/local/bin:$PATH

What is Node.js' Connect, Express and "middleware"?

Node.js itself offers an HTTP module, whose createServer method returns an object that you can use to respond to HTTP requests. That object inherits the http.Server prototype.

How to get data out of a Node.js http get request

I think it's too late to answer this question but I faced the same problem recently my use case was to call the paginated JSON API and get all the data from each pagination and append it to a single array.

const https = require('https');
const apiUrl = "";
let finaldata = [];
let someCallBack = function(data){
const getData = function (substr, pageNo=1, someCallBack) {

  let actualUrl = apiUrl + `${substr}&page=${pageNo}`;
  let mydata = []
  https.get(actualUrl, (resp) => {
    let data = '';
    resp.on('data', (chunk) => {
        data += chunk;
    resp.on('end', async () => {
        if (JSON.parse(data).total_pages!==null){
          await getData(substr, pageNo, someCallBack);
  }).on("error", (err) => {
      console.log("Error: " + err.message);

getData("spiderman", pageNo=1, someCallBack);

Like @ackuser mentioned we can use other module but In my use case I had to use the node https. Hoping this will help others.

Error: unable to verify the first certificate in nodejs

for unable to verify the first certificate in nodejs reject unauthorized is needed

 request({method: "GET", 
        "rejectUnauthorized": false, 
        "url": url,
        "headers" : {"Content-Type": "application/json",
        function(err,data,body) {

How to add items to array in nodejs

var array = [];

//length array now = 0
array[array.length] = 'hello';
//length array now = 1
//            0
//array = ['hello'];//length = 1

Create an ISO date object in javascript

Try using the ISO string

var isodate = new Date().toISOString()

See also: method definition at MDN.

How to search in array of object in mongodb

The right way is:

db.users.find({awards: {$elemMatch: {award:'National Medal', year:1975}}})

$elemMatch allows you to match more than one component within the same array element.

Without $elemMatch mongo will look for users with National Medal in some year and some award in 1975s, but not for users with National Medal in 1975.

See MongoDB $elemMatch Documentation for more info. See Read Operations Documentation for more information about querying documents with arrays.

Share variables between files in Node.js?

Save any variable that want to be shared as one object. Then pass it to loaded module so it could access the variable through object reference..

// main.js
var myModule = require('./module.js');
var shares = {value:123};

// Initialize module and pass the shareable object

// The value was changed from init2 on the other file
console.log(shares.value); // 789

On the other file..

// module.js
var shared = null;

function init2(){
    console.log(shared.value); // 123
    shared.value = 789;

module.exports = {
        // Save the shared object on current module
        shared = obj;

        // Call something outside

Check synchronously if file/directory exists in Node.js

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 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 Just open the file and handle the error when it's not there.

How can I specify the required Node.js version in package.json?

There's another, simpler way to do this:

  1. npm install Node@8 (saves Node 8 as dependency in package.json)
  2. Your app will run using Node 8 for anyone - even Yarn users!

This works because node is just a package that ships node as its package binary. It just includes as node_module/.bin which means it only makes node available to package scripts. Not main shell.

See discussion on Twitter here:

How do I install the babel-polyfill library?

This changed a bit in babel v6.

From the docs:

The polyfill will emulate a full ES6 environment. This polyfill is automatically loaded when using babel-node.

$ npm install babel-polyfill

Usage in Node / Browserify / Webpack:
To include the polyfill you need to require it at the top of the entry point to your application.

Usage in Browser:
Available from the dist/polyfill.js file within a babel-polyfill npm release. This needs to be included before all your compiled Babel code. You can either prepend it to your compiled code or include it in a <script> before it.

NOTE: Do not require this via browserify etc, use babel-polyfill.

Function to convert timestamp to human date in javascript

This is what I did for the instagram API. converted timestamp with date method by multiplying by 1000. and then added all entity individually like (year, months, etc)

created the custom month list name and mapped with getMonth() method which returns the index of the month.


// Unixtimestamp

// Months array
var months_arr = ['January','February','March','April','May','June','July','August','September','October','November','December'];

// Convert timestamp to milliseconds
var date = new Date(unixtimestamp*1000);

// Year
var year = date.getFullYear();

// Month
var month = months_arr[date.getMonth()];

// Day
var day = date.getDate();

// Hours
var hours = date.getHours();

// Minutes
var minutes = "0" + date.getMinutes();

// Seconds
var seconds = "0" + date.getSeconds();

// Display date time in MM-dd-yyyy h:m:s format
var fulldate = month+' '+day+'-'+year+' '+hours + ':' + minutes.substr(-2) + ':' + seconds.substr(-2);

// filtered fate
var convdataTime = month+' '+day;
return convdataTime;

Call with stamp argument convertStampDate('1382086394000')

and thats it.

Angular: Cannot Get /

For me it also was problem with path, but I had percentage sign in the root folder.

After I replaced %20 with space, it started to work :)

WebSocket connection failed: Error during WebSocket handshake: Unexpected response code: 400

Problem solved! I just figured out how to solve the issue, but I would still like to know if this is normal behavior or not.

It seems that even though the Websocket connection establishes correctly (indicated by the 101 Switching Protocols request), it still defaults to long-polling. The fix was as simple as adding this option to the connection function:

{transports: ['websocket']}

So the code finally looks like this:

const app = express();
const server = http.createServer(app);
var io = require('')(server);

io.on('connection', function(socket) {
  console.log('connected socket!');

  socket.on('greet', function(data) {
    socket.emit('respond', { hello: 'Hey, Mr.Client!' });
  socket.on('disconnect', function() {
    console.log('Socket disconnected');

and on the client:

var socket = io('ws://localhost:3000', {transports: ['websocket']});
socket.on('connect', function () {
  socket.emit('greet', { message: 'Hello Mr.Server!' });

socket.on('respond', function (data) {

And the messages now appear as frames:

working websockets

This Github issue pointed me in the right direction. Thanks to everyone who helped out!

Failed to load c++ bson extension

Here's how I fixed the problem on Ubuntu:

  1. ln -s /usr/bin/nodejs /usr/bin/node
  2. npm install node-gyp
  3. cd node_modules/mongodb/node_modules/bson
  4. node-gyp rebuild

Inspired by @mbochynski answer, but I had to create a symbolic link first, otherwise the rebuild failed.

Why is "npm install" really slow?

This link helped me boost npm installs. Force npm to use http over https and disable progress display.

Async/Await Class Constructor

Unlike others have said, you can get it to work.

JavaScript classes can return literally anything from their constructor, even an instance of another class. So, you might return a Promise from the constructor of your class that resolves to its actual instance.

Below is an example:

export class Foo {

    constructor() {

        return (async () => {

            // await anything you want

            return this; // Return the newly-created instance

Then, you'll create instances of Foo this way:

const foo = await new Foo();

Node.js request CERT_HAS_EXPIRED

I had this problem on production with Heroku and locally while debugging on my macbook pro this morning.

After an hour of debugging, this resolved on its own both locally and on production. I'm not sure what fixed it, so that's a bit annoying. It happened right when I thought I did something, but reverting my supposed fix didn't bring the problem back :(

Interestingly enough, it appears my database service, MongoDb has been having server problems since this morning, so there's a good chance this was related to it.

enter image description here

Properly close mongoose's connection once you're done

Probably you have this:

const db = mongoose.connect('mongodb://localhost:27017/db');

// Do some stuff


but you can also have something like this:


const model = mongoose.model('Model', ModelSchema);

model.find().then(doc => {

you cannot call db.disconnect() but you can close the connection after you use it.

model.find().then(doc => {
}).then(() => {

Install dependencies globally and locally using package.json

This is a bit old but I ran into the requirement so here is the solution I came up with.

The Problem:

Our development team maintains many .NET web application products we are migrating to AngularJS/Bootstrap. VS2010 does not lend itself easily to custom build processes and my developers are routinely working on multiple releases of our products. Our VCS is Subversion (I know, I know. I'm trying to move to Git but my pesky marketing staff is so demanding) and a single VS solution will include several separate projects. I needed my staff to have a common method for initializing their development environment without having to install the same Node packages (gulp, bower, etc.) several times on the same machine.


  1. Need "npm install" to install the global Node/Bower development environment as well as all locally required packages for a .NET product.

  2. Global packages should be installed only if not already installed.

  3. Local links to global packages must be created automatically.

The Solution:

We already have a common development framework shared by all developers and all products so I created a NodeJS script to install the global packages when needed and create the local links. The script resides in "....\SharedFiles" relative to the product base folder:

* $Id: npm-setup.js 12785 2016-01-29 16:34:49Z sthames $
* ==============================================================================
* Parameters: 'links' - Create links in local environment, optional.
* <p>NodeJS script to install common development environment packages in global
* environment. <c>packages</c> object contains list of packages to install.</p>
* <p>Including 'links' creates links in local environment to global packages.</p>
* <p><b>npm ls -g --json</b> command is run to provide the current list of 
* global packages for comparison to required packages. Packages are installed 
* only if not installed. If the package is installed but is not the required 
* package version, the existing package is removed and the required package is 
* installed.</p>.
* <p>When provided as a "preinstall" script in a "package.json" file, the "npm
* install" command calls this to verify global dependencies are installed.</p>
var exec = require('child_process').exec;
var fs   = require('fs');
var path = require('path');

/* List of packages to install and 'from' value to pass to 'npm  */
/* install'. Value must match the 'from' field in 'npm ls -json' */
/* so this script will recognize a package is already installed. */
var packages = 
  "bower"                      :                      "[email protected]", 
  "event-stream"               :               "[email protected]",
  "gulp"                       :                       "[email protected]",
  "gulp-angular-templatecache" : "[email protected]",
  "gulp-clean"                 :                 "[email protected]", 
  "gulp-concat"                :                "[email protected]",
  "gulp-debug"                 :                 "[email protected]",
  "gulp-filter"                :                "[email protected]",
  "gulp-grep-contents"         :         "[email protected]",
  "gulp-if"                    :                    "[email protected]", 
  "gulp-inject"                :                "[email protected]", 
  "gulp-minify-css"            :            "[email protected]",
  "gulp-minify-html"           :           "[email protected]",
  "gulp-minify-inline"         :         "[email protected]",
  "gulp-ng-annotate"           :           "[email protected]",
  "gulp-processhtml"           :           "[email protected]",
  "gulp-rev"                   :                   "[email protected]",
  "gulp-rev-replace"           :           "[email protected]",
  "gulp-uglify"                :                "[email protected]",
  "gulp-useref"                :                "[email protected]",
  "gulp-util"                  :                  "[email protected]",
  "lazypipe"                   :                   "[email protected]",
  "q"                          :                          "[email protected]",
  "through2"                   :                   "[email protected]",

  /* fork of 0.2.14 allows passing parameters to main-bower-files. */
  "bower-main"                 : "git+" 

* run */
* Executes <c>cmd</c> in the shell and calls <c>cb</c> on success. Error aborts.
* Note: Error code -4082 is EBUSY error which is sometimes thrown by npm for 
* reasons unknown. Possibly this is due to antivirus program scanning the file 
* but it sometimes happens in cases where an antivirus program does not explain 
* it. The error generally will not happen a second time so this method will call 
* itself to try the command again if the EBUSY error occurs.
* @param  cmd  Command to execute.
* @param  cb   Method to call on success. Text returned from stdout is input.
var run = function(cmd, cb)
  /* Increase the maxBuffer to 10MB for commands */
  /* with a lot of output. This is not necessary */
  /* with spawn but it has other issues.         */
  exec(cmd, { maxBuffer: 1000*1024 }, function(err, stdout)
    if      (!err)                   cb(stdout);
    else if (err.code | 0 == -4082) run(cmd, cb);
    else throw err;

* runCommand */
* Logs the command and calls <c>run</c>.
var runCommand = function(cmd, cb)
  run(cmd, cb);

* Main line
var doLinks  = (process.argv[2] || "").toLowerCase() == 'links';
var names    = Object.keys(packages);
var name;
var installed;
var links;

/* Get the list of installed packages for   */
/* version comparison and install packages. */
console.log('Configuring global Node environment...')
run('npm ls -g --json', function(stdout)
  installed = JSON.parse(stdout).dependencies || {};

/* Start of asynchronous package installation */
/* loop. Do until all packages installed.     */
var doWhile = function()
  if (name = names.shift())

var doWhile0 = function()
  /* Installed package specification comes from   */
  /* 'from' field of installed packages. Required */
  /* specification comes from the packages list.  */
  var current  = (installed[name] || {}).from;
  var required =   packages[name];

  /* Install the package if not installed. */
  if (!current)
    runCommand('npm install -g '+required, doWhile1);

  /* If the installed version does not  */
  /* match, uninstall and then install. */
  else if (current != required)
    delete installed[name];
    runCommand('npm remove -g '+name, function() 
      runCommand('npm remove '+name, doWhile0);

  /* Skip package if already installed. */

var doWhile1 = function()
  /* Create link to global package from local environment. */
  if (doLinks && !fs.existsSync(path.join('node_modules', name)))
    runCommand('npm link '+name, doWhile);

Now if I want to update a global tool for our developers, I update the "packages" object and check in the new script. My developers check it out and either run it with "node npm-setup.js" or by "npm install" from any of the products under development to update the global environment. The whole thing takes 5 minutes.

In addition, to configure the environment for the a new developer, they must first only install NodeJS and GIT for Windows, reboot their computer, check out the "Shared Files" folder and any products under development, and start working.

The "package.json" for the .NET product calls this script prior to install:

"name"                    : "Books",
"description"             : "Node (npm) configuration for Books Database Web Application Tools",
"version"                 : "2.1.1",
"private"                 : true,
  "preinstall"            : "node ../../SharedFiles/npm-setup.js links",
  "postinstall"           : "bower install"
"dependencies": {}


  • Note the script reference requires forward slashes even in a Windows environment.

  • "npm ls" will give "npm ERR! extraneous:" messages for all packages locally linked because they are not listed in the "package.json" "dependencies".

Edit 1/29/16

The updated npm-setup.js script above has been modified as follows:

  • Package "version" in var packages is now the "package" value passed to npm install on the command line. This was changed to allow for installing packages from somewhere other than the registered repository.

  • If the package is already installed but is not the one requested, the existing package is removed and the correct one installed.

  • For reasons unknown, npm will periodically throw an EBUSY error (-4082) when performing an install or link. This error is trapped and the command re-executed. The error rarely happens a second time and seems to always clear up.

ECONNREFUSED error when connecting to mongodb from node.js

Check this post.

It probably means that mongodb is not running. You will have to enable it through the command line or on windows run services.msc and enable mongodb.

ReadFile in Base64 Nodejs

var fs = require('fs');

function base64Encode(file) {
    var body = fs.readFileSync(file);
    return body.toString('base64');

var base64String = base64Encode('test.jpg');
console.log(base64String); + Node.js Cross-Origin Request Blocked

You can try to set origins option on the server side to allow cross-origin requests:

io.set('origins', '');

Here is the origin you want to allow requests from.

You can read more about origins format here

How to redirect 404 errors to a page in ExpressJS?

You can put a middleware at the last position that throws a NotFound error,
or even renders the 404 page directly:


How can I mock an ES6 module import using Jest?

I've been able to solve this by using a hack involving import *. It even works for both named and default exports!

For a named export:

// dependency.js
export const doSomething = (y) => console.log(y)

// myModule.js
import { doSomething } from './dependency';

export default (x) => {
  doSomething(x * 2);

// myModule-test.js
import myModule from '../myModule';
import * as dependency from '../dependency';

describe('myModule', () => {
  it('calls the dependency with double the input', () => {
    dependency.doSomething = jest.fn(); // Mutate the named export



Or for a default export:

// dependency.js
export default (y) => console.log(y)

// myModule.js
import dependency from './dependency'; // Note lack of curlies

export default (x) => {
  dependency(x * 2);

// myModule-test.js
import myModule from '../myModule';
import * as dependency from '../dependency';

describe('myModule', () => {
  it('calls the dependency with double the input', () => {
    dependency.default = jest.fn(); // Mutate the default export


    expect(dependency.default).toBeCalledWith(4); // Assert against the default

As Mihai Damian quite rightly pointed out below, this is mutating the module object of dependency, and so it will 'leak' across to other tests. So if you use this approach you should store the original value and then set it back again after each test.

To do this easily with Jest, use the spyOn() method instead of jest.fn(), because it supports easily restoring its original value, therefore avoiding before mentioned 'leaking'.

Node / Express: EADDRINUSE, Address already in use - Kill server

bash$ sudo netstat -ltnp | grep -w ':3000'
 - tcp6    0      0 :::4000      :::*        LISTEN      31157/node      

bash$ kill 31157

How do I debug "Error: spawn ENOENT" on node.js?

Although it may be an environment path or another issue for some people, I had just installed the Latex Workshop extension for Visual Studio Code on Windows 10 and saw this error when attempting to build/preview the PDF. Running VS Code as Administrator solved the problem for me.

node.js execute system command synchronously

Just to add that even though there are few usecases where you should use them, spawnSync / execFileSync / execSync were added to node.js in these commits:

How can I update NodeJS and NPM to the next versions?

Use n module from npm in order to upgrade node . n is a node helper package that installs or updates a given node.js version.

sudo npm cache clean -f
sudo npm install -g n
sudo n stable
sudo ln -sf /usr/local/n/versions/node/<VERSION>/bin/node /usr/bin/nodejs

NOTE that the default installation for nodejs is in the /usr/bin/nodejs and not /usr/bin/node

To upgrade to latest version (and not current stable) version, you can use

sudo n latest

To undo:

sudo apt-get install --reinstall nodejs-legacy     # fix /usr/bin/node
sudo n rm 6.0.0     # replace number with version of Node that was installed
sudo npm uninstall -g n

If you get the following error bash: /usr/bin/node: No such file or directory then the path you have entered at

sudo ln -sf /usr/local/n/versions/node/<VERSION>/bin/node /usr/bin/nodejs

if wrong. so make sure to check if the update nodejs has been installed at the above path and the version you are entered is correct.

I would advise strongly against doing this on a production instance. It can seriously mess stuff up with your global npm packages and your ability to install new one.

Node Sass couldn't find a binding for your current environment

I have tried all methods I've found.

I have noticed some strange behavior of that folder. When I was trying to "cd" to 'node_sass' folder from VS terminal, it told that "Folder was not found", but was seen in Finder.

chmod from VS terminal haven't find folder even with 'sudo' command.

I have chmod-ed from native MacOs terminal and just after have rebuild with node.

Formatting ISODate from Mongodb

// from MongoDate object to Javascript Date object

var MongoDate = {sec: 1493016016, usec: 650000};
var dt = new Date("1970-01-01T00:00:00+00:00");

How to make a node.js application run permanently?

I'd recommend looking for something such as Forever to restart Node in the event of a crash, and handle daemonizing this for you.

Invalid shorthand property initializer

Change the = to : to fix the error.

var makeRequest = function(message) {<br>
 var options = {<br>
  host: 'localhost',<br>
  port : 8080,<br>
  path : '/',<br>
  method: 'POST'<br>

Setting Environment Variables for Node to retrieve

Environment variables (in this case) are being used to pass credentials to your application. USER_ID and USER_KEY can both be accessed from process.env.USER_ID and process.env.USER_KEY respectively. You don't need to edit them, just access their contents.

It looks like they are simply giving you the choice between loading your USER_ID and USER_KEY from either process.env or some specificed file on disk.

Now, the magic happens when you run the application.

USER_ID=239482 USER_KEY=foobar node app.js

That will pass the user id 239482 and the user key as foobar. This is suitable for testing, however for production, you will probably be configuring some bash scripts to export variables.

Upgrade Node.js to the latest version on Mac OS

Easy nad Safe Steps

Step 1: Install NVM

brew install nvm

Step 2: Create a directory for NVM

mkdir ~/.nvm/

Step 3: Configure your environmental variables

nano ~/.bash_profile


export NVM_DIR=~/.nvm
source $(brew --prefix nvm)/

source ~/.bash_profile

Step 4: Double check your work

nvm ls

Step 5: Install Node

nvm install 9.x.x

Step6: Upgrade

nvm ls-remote

   v10.16.2   (LTS: Dubnium)
   v10.16.3   (Latest LTS: Dubnium) ..........

nvm install v10.16.3


Error Example #1
rm -rf /usr/local/lib/node_modules
brew uninstall node
brew install node --without-npm
echo prefix=~/.npm-packages >> ~/.npmrc
curl -L | sh

How do I parse a HTML page with Node.js

Use Cheerio. It isn't as strict as jsdom and is optimized for scraping. As a bonus, uses the jQuery selectors you already know.

? Familiar syntax: Cheerio implements a subset of core jQuery. Cheerio removes all the DOM inconsistencies and browser cruft from the jQuery library, revealing its truly gorgeous API.

? Blazingly fast: Cheerio works with a very simple, consistent DOM model. As a result parsing, manipulating, and rendering are incredibly efficient. Preliminary end-to-end benchmarks suggest that cheerio is about 8x faster than JSDOM.

? Insanely flexible: Cheerio wraps around @FB55's forgiving htmlparser. Cheerio can parse nearly any HTML or XML document.

How to build minified and uncompressed bundle with webpack?

To add another answer, the flag -p (short for --optimize-minimize) will enable the UglifyJS with default arguments.

You won't get a minified and raw bundle out of a single run or generate differently named bundles so the -p flag may not meet your use case.

Conversely the -d option is short for --debug --devtool sourcemap --output-pathinfo

My webpack.config.js omits devtool, debug, pathinfo, and the minmize plugin in favor of these two flags.

Streaming a video file to an html5 video player with Node.js so that the video controls continue to work?

The accepted answer to this question is awesome and should remain the accepted answer. However I ran into an issue with the code where the read stream was not always being ended/closed. Part of the solution was to send autoClose: true along with start:start, end:end in the second createReadStream arg.

The other part of the solution was to limit the max chunksize being sent in the response. The other answer set end like so:

var end = positions[1] ? parseInt(positions[1], 10) : total - 1;

...which has the effect of sending the rest of the file from the requested start position through its last byte, no matter how many bytes that may be. However the client browser has the option to only read a portion of that stream, and will, if it doesn't need all of the bytes yet. This will cause the stream read to get blocked until the browser decides it's time to get more data (for example a user action like seek/scrub, or just by playing the stream).

I needed this stream to be closed because I was displaying the <video> element on a page that allowed the user to delete the video file. However the file was not being removed from the filesystem until the client (or server) closed the connection, because that is the only way the stream was getting ended/closed.

My solution was just to set a maxChunk configuration variable, set it to 1MB, and never pipe a read a stream of more than 1MB at a time to the response.

// same code as accepted answer
var end = positions[1] ? parseInt(positions[1], 10) : total - 1;
var chunksize = (end - start) + 1;

// poor hack to send smaller chunks to the browser
var maxChunk = 1024 * 1024; // 1MB at a time
if (chunksize > maxChunk) {
  end = start + maxChunk - 1;
  chunksize = (end - start) + 1;

This has the effect of making sure that the read stream is ended/closed after each request, and not kept alive by the browser.

I also wrote a separate StackOverflow question and answer covering this issue.

File uploading with Express 4.0: req.files undefined

The body-parser module only handles JSON and urlencoded form submissions, not multipart (which would be the case if you're uploading files).

For multipart, you'd need to use something like connect-busboy or multer or connect-multiparty (multiparty/formidable is what was originally used in the express bodyParser middleware). Also FWIW, I'm working on an even higher level layer on top of busboy called reformed. It comes with an Express middleware and can also be used separately.

How to access the request body when POSTing using Node.js and Express?

This can be achieved without body-parser dependency as well, listen to request:data and request:end and return the response on end of request, refer below code sample. ref:

var express = require('express');
var app = express.createServer(express.logger());'/', function(request, response) {

    // push the data to body
    var body = [];
    request.on('data', (chunk) => {
    }).on('end', () => {
      // on end of data, perform necessary action
      body = Buffer.concat(body).toString();

What is the "__v" field in Mongoose

For remove in NestJS need to add option to Shema() decorator

@Schema({ versionKey: false })

Passing route control with optional parameter after root in express?

Express version:

"dependencies": {
    "body-parser": "^1.19.0",
    "express": "^4.17.1"

Optional parameter are very much handy, you can declare and use them easily using express:

app.get('/api/v1/tours/:cId/:pId/:batchNo?', (req, res)=>{
    console.log("category Id: "+req.params.cId);
    console.log("product ID: "+req.params.pId);
    if (req.params.batchNo){
        console.log("Batch No: "+req.params.batchNo);

In the above code batchNo is optional. Express will count it optional because after in URL construction, I gave a '?' symbol after batchNo '/:batchNo?'

Now I can call with only categoryId and productId or with all three-parameter.

enter image description here enter image description here

Node.js Generate html

You can use jsdom

const jsdom = require("jsdom");
const { JSDOM } = jsdom;
const { document } = (new JSDOM(`...`)).window;

or, take a look at cheerio, it may more suitable in your case.

Mongoose: Get full list of users

There was the very easy way to list your data :

server.get('/userlist' , function (req , res) {
 User.find({}).then(function (users) {

Is there a template engine for Node.js?

You can try beardless (it's inspired by weld/plates):

For example:

{ post:
  { title: "Next generation templating: Start shaving!"
  , text: "TL;DR You should really check out beardless!"
  , comments:
    [ {text: "Hey cool!"}
    , {text: "Really gotta check that out..."}  ]

Your template:

<h1 data-template="post.title"></h1>
<p data-template="post.text"></p>
  <div data-template="post.comments" class="comment">
    <p data-template="post.comments.text"></p>


<h1>Next generation templating: Start shaving!</h1>
<p>TL;DR You should really check out beardless!</p>
  <div class="comment">
    <p>Hey cool!</p>
  <div class="comment">
    <p>Really gotta check that out...</p>

nodemon not working: -bash: nodemon: command not found

sudo su


npm install nodemon 

worked for me

How can I get npm start at a different directory?

npm start --prefix path/to/your/app

& inside package.json add the following script

"scripts": {
   "preinstall":"cd $(pwd)"

NodeJS/express: Cache and 304 status code

Old question, I know. Disabling the cache facility is not needed and not the best way to manage the problem. By disabling the cache facility the server needs to work harder and generates more traffic. Also the browser and device needs to work harder, especially on mobile devices this could be a problem.

The empty page can be easily solved by using Shift key+reload button at the browser.

The empty page can be a result of:

  • a bug in your code
  • while testing you served an empty page (you can't remember) that is cached by the browser
  • a bug in Safari (if so, please report it to Apple and don't try to fix it yourself)

Try first the Shift keyboard key + reload button and see if the problem still exists and review your code.

How can I uninstall npm modules in Node.js?

If it doesn't work with npm uninstall <module_name> try it globally by typing -g.

Maybe you just need to do it as an superUser/administrator with sudo npm uninstall <module_name>.

Sending command line arguments to npm script

From what I see, people use package.json scripts when they would like to run script in simpler way. For example, to use nodemon that installed in local node_modules, we can't call nodemon directly from the cli, but we can call it by using ./node_modules/nodemon/nodemon.js. So, to simplify this long typing, we can put this...


    scripts: {
      'start': 'nodemon app.js'


... then call npm start to use 'nodemon' which has app.js as the first argument.

What I'm trying to say, if you just want to start your server with the node command, I don't think you need to use scripts. Typing npm start or node app.js has the same effort.

But if you do want to use nodemon, and want to pass a dynamic argument, don't use script either. Try to use symlink instead.

For example using migration with sequelize. I create a symlink...

ln -s node_modules/sequelize/bin/sequelize sequelize

... And I can pass any arguement when I call it ...

./sequlize -h /* show help */

./sequelize -m /* upgrade migration */

./sequelize -m -u /* downgrade migration */


At this point, using symlink is the best way I could figure out, but I don't really think it's the best practice.

I also hope for your opinion to my answer.

npm global path prefix

I managed to fix Vue Cli no command error by doing the following:

  • In terminal sudo nano ~/.bash_profile to edit your bash profile.
  • Add export PATH=$PATH:/Users/[your username]/.npm-packages/bin
  • Save file and restart terminal
  • Now you should be able to use vue create my-project and vue --version etc.

I did this after I installed the latest Vue Cli from

I generally use yarn, but I installed this globally with npm npm install -g @vue/cli. You can use yarn too if you'd like yarn global add @vue/cli

Note: you may have to uninstall it first globally if you already have it installed: npm uninstall -g vue-cli

Hope this helps!

Renaming files using node.js

You'll need to use fs for that:

And in particular the fs.rename() function:

var fs = require('fs');
fs.rename('/path/to/Afghanistan.png', '/path/to/AF.png', function(err) {
    if ( err ) console.log('ERROR: ' + err);

Put that in a loop over your freshly-read JSON object's keys and values, and you've got a batch renaming script.

fs.readFile('/path/to/countries.json', function(error, data) {
    if (error) {

    var obj = JSON.parse(data);
    for(var p in obj) {
        fs.rename('/path/to/' + obj[p] + '.png', '/path/to/' + p + '.png', function(err) {
            if ( err ) console.log('ERROR: ' + err);

(This assumes here that your .json file is trustworthy and that it's safe to use its keys and values directly in filenames. If that's not the case, be sure to escape those properly!)

Get the client's IP address in

Very easy. First put

io.sockets.on('connection', function (socket) {


You will see all fields of socket. then use CTRL+F and search the word address. Finally, when you find the field remoteAddress use dots to filter data. in my case it is


nodeJs callbacks simple example

Try this example as simple as you can read, just copy save newfile.js do node newfile to run the application.

function myNew(next){
    console.log("Im the one who initates callback");
    next("nope", "success");

myNew(function(err, res){
    console.log("I got back from callback",err, res);

NPM global install "cannot find module"

The following generic fix would for any module. For example with request-promise.


npm install request-promise --global


npm install request-promise --cli

worked (source) and also for globals and inherits

Also, try setting the environment variable


How to set cookie in node js using express framework?

Not exactly answering your question, but I came across your question, while looking for an answer to an issue that I had. Maybe it will help somebody else.

My issue was that cookies were set in server response, but were not saved by the browser.

The server response came back with cookies set:

Set-Cookie:my_cookie=HelloWorld; Path=/; Expires=Wed, 15 Mar 2017 15:59:59 GMT 

This is how I solved it.

I used fetch in the client-side code. If you do not specify credentials: 'include' in the fetch options, cookies are neither sent to server nor saved by the browser, even though the server response sets cookies.


var headers = new Headers();
headers.append('Content-Type', 'application/json');
headers.append('Accept', 'application/json');

return fetch('/your/server_endpoint', {
    method: 'POST',
    mode: 'same-origin',
    redirect: 'follow',
    credentials: 'include', // Don't forget to specify this if you need cookies
    headers: headers,
    body: JSON.stringify({
        first_name: 'John',
        last_name: 'Doe'

I hope this helps somebody.

Error: request entity too large

I faced the same issue recently and bellow solution workes for me.

Dependency : 
express >> version : 4.17.1
body-parser >> version": 1.19.0
const express = require('express');
const bodyParser = require('body-parser');

const app = express(); 
app.use(bodyParser.json({limit: '50mb'}));
app.use(bodyParser.urlencoded({limit: '50mb', extended: true}));

For understanding : HTTP 431

The HTTP 413 Payload Too Large response status code indicates that the request entity is larger than limits defined by server; the server might close the connection or return a Retry-After header field.

How to decide when to use Node.js?

The most important reasons to start your next project using Node ...

  • All the coolest dudes are into it ... so it must be fun.
  • You can hangout at the cooler and have lots of Node adventures to brag about.
  • You're a penny pincher when it comes to cloud hosting costs.
  • Been there done that with Rails
  • You hate IIS deployments
  • Your old IT job is getting rather dull and you wish you were in a shiny new Start Up.

What to expect ...

  • You'll feel safe and secure with Express without all the server bloatware you never needed.
  • Runs like a rocket and scales well.
  • You dream it. You installed it. The node package repo is the largest ecosystem of open source libraries in the world.
  • Your brain will get time warped in the land of nested callbacks ...
  • ... until you learn to keep your Promises.
  • Sequelize and Passport are your new API friends.
  • Debugging mostly async code will get umm ... interesting .
  • Time for all Noders to master Typescript.

Who uses it?

  • PayPal, Netflix, Walmart, LinkedIn, Groupon, Uber, GoDaddy, Dow Jones
  • Here's why they switched to Node.

How to install npm peer dependencies automatically?

The project npm-install-peers will detect peers and install them.

As of v1.0.1 it doesn't support writing back to the package.json automatically, which would essentially solve our need here.

Please add your support to issue in flight:

await is only valid in async function

The current implementation of async / await only supports the await keyword inside of async functions Change your start function signature so you can use await inside start.

 var start = async function(a, b) {


For those interested, the proposal for top-level await is currently in Stage 2:

Node.js: get path from the request

req.protocol + '://' + req.get('host') + req.originalUrl


req.protocol + '://' + + req.originalUrl // I like this one as it survives from proxy server, getting the original host name

Connect to SQL Server database from Node.js

We just released preview driver for Node.JS for SQL Server connectivity. You can find it here: Introducing the Microsoft Driver for Node.JS for SQL Server.

The driver supports callbacks (here, we're connecting to a local SQL Server instance):

// Query with explicit connection
var sql = require('node-sqlserver');
var conn_str = "Driver={SQL Server Native Client 11.0};Server=(local);Database=AdventureWorks2012;Trusted_Connection={Yes}";, function (err, conn) {
    if (err) {
        console.log("Error opening the connection!");
    conn.queryRaw("SELECT TOP 10 FirstName, LastName FROM Person.Person", function (err, results) {
        if (err) {
            console.log("Error running query!");
        for (var i = 0; i < results.rows.length; i++) {
            console.log("FirstName: " + results.rows[i][0] + " LastName: " + results.rows[i][1]);

Alternatively, you can use events (here, we're connecting to SQL Azure a.k.a Windows Azure SQL Database):

// Query with streaming
var sql = require('node-sqlserver');
var conn_str = "Driver={SQL Server Native Client 11.0};Server={,1433};UID={username};PWD={Password1};Encrypt={Yes};Database={databasename}";

var stmt = sql.query(conn_str, "SELECT FirstName, LastName FROM Person.Person ORDER BY LastName OFFSET 0 ROWS FETCH NEXT 10 ROWS ONLY");
stmt.on('meta', function (meta) { console.log("We've received the metadata"); });
stmt.on('row', function (idx) { console.log("We've started receiving a row"); });
stmt.on('column', function (idx, data, more) { console.log(idx + ":" + data);});
stmt.on('done', function () { console.log("All done!"); });
stmt.on('error', function (err) { console.log("We had an error :-( " + err); });

If you run into any problems, please file an issue on Github:

Cannot overwrite model once compiled Mongoose

There is another way to throw this error.

Keep in mind that the path to the model is case sensitive.

In this similar example involving the "Category" model, the error was thrown under these conditions:

1) The require statement was mentioned in two files: ..category.js and ..index.js 2) I the first, the case was correct, in the second file it was not as follows:


enter image description here


enter image description here

How to host a Node.Js application in shared hosting

You should look for a hosting company that provides such feature, but standard simple static+PHP+MySQL hosting won't let you use node.js.

You need either find a hosting designed for node.js or buy a Virtual Private Server and install it yourself.

What is the suggested way to install brew, node.js, io.js, nvm, npm on OS X?

Here's what I do:

curl | bash
cd / && . ~/.nvm/ && nvm install 0.10.35
. ~/.nvm/ && nvm alias default 0.10.35

No Homebrew for this one.

nvm soon will support io.js, but not at time of posting:

Then install everything else, per-project, with a package.json and npm install.

Parsing a CSV file using NodeJS

The node-csv project that you are referencing is completely sufficient for the task of transforming each row of a large portion of CSV data, from the docs at:

  .transform(function(row, index, callback){
      callback(null, row.reverse());

From my experience, I can say that it is also a rather fast implementation, I have been working with it on data sets with near 10k records and the processing times were at a reasonable tens-of-milliseconds level for the whole set.

Rearding jurka's stream based solution suggestion: node-csv IS stream based and follows the Node.js' streaming API.

env: node: No such file or directory in mac

Let's see, I sorted that on a different way. in my case I had as path something like ~/.local/bin which seems that it is not the way it wants.

Try to use the full path, like /Users/tobias/.local/bin, I mean, change the PATH variable from ~/.local/bin to /Users/tobias/.local/bin or $HOME/.local/bin .

Now it works.

npm ERR! Error: EPERM: operation not permitted, rename

I was getting that same error and according to it could be caused by your antivirus software. I disabled mine for the duration of the install and executed "npm install" on cmd as admin and it worked. Hope this helps.

E: Unable to locate package npm

From the official Node.js documentation:

A Node.js package is also available in the official repo for Debian Sid (unstable), Jessie (testing) and Wheezy (wheezy-backports) as "nodejs". It only installs a nodejs binary.

So, if you only type sudo apt-get install nodejs , it does not install other goodies such as npm.

You need to type:

curl -sL | sudo -E bash -
sudo apt-get install -y nodejs

Optional: install build tools

To compile and install native add-ons from npm you may also need to install build tools:

sudo apt-get install -y build-essential

More info: Docs

Loading basic HTML in Node.js

It's more flexible and simple way to use pipe method.

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

http.createServer(function(request, response) {
  response.writeHead(200, {'Content-Type': 'text/html'});

  var file = fs.createReadStream('index.html');


console.log('listening on port 8080...');

Exec : display stdout "live"

exec will also return a ChildProcess object that is an EventEmitter.

var exec = require('child_process').exec;
var coffeeProcess = exec('coffee -cw');

coffeeProcess.stdout.on('data', function(data) {

OR pipe the child process's stdout to the main stdout.


OR inherit stdio using spawn

spawn('coffee -cw', { stdio: 'inherit' });

Nodejs cannot find installed module on Windows

I had a terrible time getting global modules to work. Eventually, I explicitly added C:\Users\yourusername\AppData\Roaming\npm to the PATH variable under System Variables. I also needed to have this variable come before the nodejs path variable in the list.

I am running Windows 10.

fs.writeFile in a promise, asynchronous-synchronous stuff

Finally, the latest node.js release v10.3.0 has natively supported fs promises.

const fsPromises = require('fs').promises; // or require('fs/promises') in v10.0.0
fsPromises.writeFile(ASIN + '.json', JSON.stringify(results))
  .then(() => {
    console.log('JSON saved');
  .catch(er => {

You can check the official documentation for more details.

How to monitor the memory usage of Node.js?

Also, if you'd like to know global memory rather than node process':

var os = require('os');


See documentation

npm WARN notsup SKIPPING OPTIONAL DEPENDENCY: Unsupported platform for [email protected]

This still appears to be an issue, causing package installations to be aborted with warnings about optional packages no being installed because of "Unsupported platform".

The problem relates to the "shrinkwrap" or package-lock.json which gets persisted after every package manager execution. Subsequent attempts keep failing as this file is referenced instead of package.json.

Adding these options to the npm install command should allow packages to install again.

   --no-optional argument will prevent optional dependencies from being installed.

   --no-shrinkwrap argument, which will ignore an available package lock or
                   shrinkwrap file and use the package.json instead.

   --no-package-lock argument will prevent npm from creating a package-lock.json file.

The complete command looks like this:

    npm install --no-optional --no-shrinkwrap --no-package-lock


How to run a shell script at startup

Just have a line added to your crontab..

Make sure the file is executable:

chmod +x /path_to_you_file/your_file

To edit crontab file:

crontab -e

Line you have to add:

@reboot  /path_to_you_file/your_file

That simple!

String contains another string

You can use .indexOf():

if(str.indexOf(substr) > -1) {


How can I save a base64-encoded image to disk?

Easy way to convert base64 image into file and save as some random id or name.

// to create some random id or name for your image name
const imgname = new Date().getTime().toString();

// to declare some path to store your converted image
const path = yourpath.png    

// image takes from body which you uploaded
const imgdata = req.body.image;    

// to convert base64 format into random filename
const base64Data = imgdata.replace(/^data:([A-Za-z-+/]+);base64,/, '');
fs.writeFile(path, base64Data, 'base64', (err) => {

// assigning converted image into your database
req.body.coverImage = imgname

How to create a simple http proxy in node.js?

Here's an implementation using node-http-proxy from nodejitsu.

var http = require('http');
var httpProxy = require('http-proxy');
var proxy = httpProxy.createProxyServer({});

http.createServer(function(req, res) {
    proxy.web(req, res, { target: '' });

Is it not possible to stringify an Error using JSON.stringify?

None of the answers above seemed to properly serialize properties which are on the prototype of Error (because getOwnPropertyNames() does not include inherited properties). I was also not able to redefine the properties like one of the answers suggested.

This is the solution I came up with - it uses lodash but you could replace lodash with generic versions of those functions.

 function recursivePropertyFinder(obj){
    if( obj === Object.prototype){
        return {};
        return _.reduce(Object.getOwnPropertyNames(obj), 
            function copy(result, value, key) {
                if( !_.isFunction(obj[value])){
                    if( _.isObject(obj[value])){
                        result[value] = recursivePropertyFinder(obj[value]);
                        result[value] = obj[value];
                return result;
            }, recursivePropertyFinder(Object.getPrototypeOf(obj)));

Error.prototype.toJSON = function(){
    return recursivePropertyFinder(this);

Here's the test I did in Chrome:

var myError = Error('hello');
myError.causedBy = Error('error2');
myError.causedBy.causedBy = Error('error3');
myError.causedBy.causedBy.displayed = true;

{"name":"Error","message":"hello","stack":"Error: hello\n    at <anonymous>:66:15","causedBy":{"name":"Error","message":"error2","stack":"Error: error2\n    at <anonymous>:67:20","causedBy":{"name":"Error","message":"error3","stack":"Error: error3\n    at <anonymous>:68:29","displayed":true}}}  

Display rows with one or more NaN values in pandas dataframe

You can use DataFrame.any with parameter axis=1 for check at least one True in row by DataFrame.isna with boolean indexing:

df1 = df[df.isna().any(axis=1)]

d = {'filename': ['M66_MI_NSRh35d32kpoints.dat', 'F71_sMI_DMRI51d.dat', 'F62_sMI_St22d7.dat', 'F41_Car_HOC498d.dat', 'F78_MI_547d.dat'], 'alpha1': [0.8016, 0.0, 1.721, 1.167, 1.897], 'alpha2': [0.9283, 0.0, 3.833, 2.809, 5.459], 'gamma1': [1.0, np.nan, 0.23748000000000002, 0.36419, 0.095319], 'gamma2': [0.074804, 0.0, 0.15, 0.3, np.nan], 'chi2min': [39.855990000000006, 1e+25, 10.91832, 7.966335000000001, 25.93468]}
df = pd.DataFrame(d).set_index('filename')

print (df)
                             alpha1  alpha2    gamma1    gamma2       chi2min
M66_MI_NSRh35d32kpoints.dat  0.8016  0.9283  1.000000  0.074804  3.985599e+01
F71_sMI_DMRI51d.dat          0.0000  0.0000       NaN  0.000000  1.000000e+25
F62_sMI_St22d7.dat           1.7210  3.8330  0.237480  0.150000  1.091832e+01
F41_Car_HOC498d.dat          1.1670  2.8090  0.364190  0.300000  7.966335e+00
F78_MI_547d.dat              1.8970  5.4590  0.095319       NaN  2.593468e+01


print (df.isna())
                            alpha1 alpha2 gamma1 gamma2 chi2min
M66_MI_NSRh35d32kpoints.dat  False  False  False  False   False
F71_sMI_DMRI51d.dat          False  False   True  False   False
F62_sMI_St22d7.dat           False  False  False  False   False
F41_Car_HOC498d.dat          False  False  False  False   False
F78_MI_547d.dat              False  False  False   True   False

print (df.isna().any(axis=1))
M66_MI_NSRh35d32kpoints.dat    False
F71_sMI_DMRI51d.dat             True
F62_sMI_St22d7.dat             False
F41_Car_HOC498d.dat            False
F78_MI_547d.dat                 True
dtype: bool

df1 = df[df.isna().any(axis=1)]
print (df1)
                     alpha1  alpha2    gamma1  gamma2       chi2min
F71_sMI_DMRI51d.dat   0.000   0.000       NaN     0.0  1.000000e+25
F78_MI_547d.dat       1.897   5.459  0.095319     NaN  2.593468e+01

java.lang.IllegalStateException: Only fullscreen opaque activities can request orientation

I had the same problem, and my solution was to eliminate the line


and then add this in the activity:

if (android.os.Build.VERSION.SDK_INT < Build.VERSION_CODES.O) {

How to move the cursor word by word in the OS X Terminal

Use Natural Text Editing preset!

enter image description here

Essentially it binds, among other key sequences, Option + LeftArrow to ^[b sequence and Option + RightArrow to ^[f

This works in fish and bash, as well as in psql terminal.

How to keep one variable constant with other one changing with row in excel

There are two kinds of cell reference, and it's really valuable to understand them well.

One is relative reference, which is what you get when you just type the cell: A5. This reference will be adjusted when you paste or fill the formula into other cells.

The other is absolute reference, and you get this by adding dollar signs to the cell reference: $A$5. This cell reference will not change when pasted or filled.

A cool but rarely used feature is that row and column within a single cell reference may be independent: $A5 and A$5. This comes in handy for producing things like multiplication tables from a single formula.

Disable vertical scroll bar on div overflow: auto

Add the following:


Android List View Drag and Drop sort

I recently stumbled upon this great Gist that gives a working implementation of a drag sort ListView, with no external dependencies needed.

Basically it consists on creating your custom Adapter extending ArrayAdapter as an inner class to the activity containing your ListView. On this adapter one then sets an onTouchListener to your List Items that will signal the start of the drag.

In that Gist they set the listener to a specific part of the layout of the List Item (the "handle" of the item), so one does not accidentally move it by pressing any part of it. Personally, I preferred to go with an onLongClickListener instead, but that is up to you to decide. Here an excerpt of that part:

public class MyArrayAdapter extends ArrayAdapter<String> {

    private ArrayList<String> mStrings = new ArrayList<String>();
    private LayoutInflater mInflater;
    private int mLayout;

    //constructor, clear, remove, add, insert...

    public View getView(final int position, View convertView, ViewGroup parent) {
        ViewHolder holder;

        View view = convertView;
        //inflate, etc...

        final String string = mStrings.get(position);

        // Here the listener is set specifically to the handle of the layout
        holder.handle.setOnTouchListener(new View.OnTouchListener() {
            public boolean onTouch(View view, MotionEvent motionEvent) {
                if (motionEvent.getAction() == MotionEvent.ACTION_DOWN) {
                    return true;
                return false;

        // change color on dragging item and other things...         

        return view;

This also involves adding an onTouchListener to the ListView, which checks if an item is being dragged, handles the swapping and invalidation, and stops the drag state. An excerpt of that part:

mListView.setOnTouchListener(new View.OnTouchListener() {
     public boolean onTouch(View view, MotionEvent event) {
        if (!mSortable) { return false; }
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN: {
            case MotionEvent.ACTION_MOVE: {
                // get positions
                int position = mListView.pointToPosition((int) event.getX(), 
                    (int) event.getY());
                if (position < 0) {
                // check if it's time to swap
                if (position != mPosition) {
                    mPosition = position;
                    mAdapter.insert(mDragString, mPosition);
                return true;
            case MotionEvent.ACTION_UP:
            case MotionEvent.ACTION_CANCEL:
            case MotionEvent.ACTION_OUTSIDE: {
                //stop drag state
                return true;
        return false;

Finally, here is how the stopDrag and startDrag methods look like, which handle the enabling and disabling of the drag process:

public void startDrag(String string) {
    mPosition = -1;
    mSortable = true;
    mDragString = string;

public void stopDrag() {
    mPosition = -1;
    mSortable = false;
    mDragString = null;

how to write an array to a file Java

If you're okay with Apache commons lib

outputWriter.write(ArrayUtils.join(array, ","));

Why do python lists have pop() but not push()

Because it appends an element to a list? Push is usually used when referring to stacks.

Best Practice: Initialize JUnit class fields in setUp() or at declaration?

  • The constant values (uses in fixtures or assertions) should be initialized in their declarations and final (as never change)

  • the object under test should be initialized in the setup method because we may set things on. Of course we may not set something now but we could set it later. Instantiating in the init method would ease the changes.

  • dependencies of the object under test if these are mocked, should not even be instantiated by yourself : today the mock frameworks can instantiate it by reflection.

A test without dependency to mock could look like :

public class SomeTest {

    Some some; //instance under test
    static final String GENERIC_ID = "123";
    static final String PREFIX_URL_WS = "";

    public void beforeEach() {
       some = new Some(new Foo(), new Bar());

    public void populateList()

A test with dependencies to isolate could look like :

public class SomeTest {

    Some some; //instance under test
    static final String GENERIC_ID = "123";
    static final String PREFIX_URL_WS = "";

    Foo fooMock;

    Bar barMock;

    public void beforeEach() {
       some = new Some(fooMock, barMock);

    public void populateList()

How do files get into the External Dependencies in Visual Studio C++?

The External Dependencies folder is populated by IntelliSense: the contents of the folder do not affect the build at all (you can in fact disable the folder in the UI).

You need to actually include the header (using a #include directive) to use it. Depending on what that header is, you may also need to add its containing folder to the "Additional Include Directories" property and you may need to add additional libraries and library folders to the linker options; you can set all of these in the project properties (right click the project, select Properties). You should compare the properties with those of the project that does build to determine what you need to add.

Click to call html

tl;dr What to do in modern (2018) times? Assume tel: is supported, use it and forget about anything else.

The tel: URI scheme RFC5431 (as well as sms: but also feed:, maps:, youtube: and others) is handled by protocol handlers (as mailto: and http: are).

They're unrelated to HTML5 specification (it has been out there from 90s and documented first time back in 2k with RFC2806) then you can't check for their support using tools as modernizr. A protocol handler may be installed by an application (for example Skype installs a callto: protocol handler with same meaning and behaviour of tel: but it's not a standard), natively supported by browser or installed (with some limitations) by website itself.

What HTML5 added is support for installing custom web based protocol handlers (with registerProtocolHandler() and related functions) simplifying also the check for their support through isProtocolHandlerRegistered() function.

There is some easy ways to determine if there is an handler or not:" How to detect browser's protocol handlers?).

In general what I suggest is:

  1. If you're running on a mobile device then you can safely assume tel: is supported (yes, it's not true for very old devices but IMO you can ignore them).
  2. If JS isn't active then do nothing.
  3. If you're running on desktop browsers then you can use one of the techniques in the linked post to determine if it's supported.
  4. If tel: isn't supported then change links to use callto: and repeat check desctibed in 3.
  5. If tel: and callto: aren't supported (or - in a desktop browser - you can't detect their support) then simply remove that link replacing URL in href with javascript:void(0) and (if number isn't repeated in text span) putting, telephone number in title. Here HTML5 microdata won't help users (just search engines). Note that newer versions of Skype handle both callto: and tel:.

Please note that (at least on latest Windows versions) there is always a - fake - registered protocol handler called App Picker (that annoying window that let you choose with which application you want to open an unknown file). This may vanish your tests so if you don't want to handle Windows environment as a special case you can simplify this process as:

  1. If you're running on a mobile device then assume tel: is supported.
  2. If you're running on desktop then replace tel: with callto:. then drop tel: or leave it as is (assuming there are good chances Skype is installed).

Search for one value in any column of any table inside a database


I have a solution from a while ago that I kept improving. Also searches within XML columns if told to do so, or searches integer values if providing a integer only string.

/* Reto Egeter, */

DECLARE @SearchStrTableName nvarchar(255), @SearchStrColumnName nvarchar(255), @SearchStrColumnValue nvarchar(255), @SearchStrInXML bit, @FullRowResult bit, @FullRowResultRows int
SET @SearchStrColumnValue = '%searchthis%' /* use LIKE syntax */
SET @FullRowResult = 1
SET @FullRowResultRows = 3
SET @SearchStrTableName = NULL /* NULL for all tables, uses LIKE syntax */
SET @SearchStrColumnName = NULL /* NULL for all columns, uses LIKE syntax */
SET @SearchStrInXML = 0 /* Searching XML data may be slow */

IF OBJECT_ID('tempdb..#Results') IS NOT NULL DROP TABLE #Results
CREATE TABLE #Results (TableName nvarchar(128), ColumnName nvarchar(128), ColumnValue nvarchar(max),ColumnType nvarchar(20))


DECLARE @TableName nvarchar(256) = '',@ColumnName nvarchar(128),@ColumnType nvarchar(20), @QuotedSearchStrColumnValue nvarchar(110), @QuotedSearchStrColumnName nvarchar(110)
SET @QuotedSearchStrColumnValue = QUOTENAME(@SearchStrColumnValue,'''')
DECLARE @ColumnNameTable TABLE (COLUMN_NAME nvarchar(128),DATA_TYPE nvarchar(20))

SET @TableName =
WHERE TABLE_SCHEMA = PARSENAME(''' + @TableName + ''', 2)
AND TABLE_NAME = PARSENAME(''' + @TableName + ''', 1)
AND DATA_TYPE IN (' + CASE WHEN ISNUMERIC(REPLACE(REPLACE(REPLACE(REPLACE(REPLACE(@SearchStrColumnValue,'%',''),'_',''),'[',''),']',''),'-','')) = 1 THEN '''tinyint'',''int'',''smallint'',''bigint'',''numeric'',''decimal'',''smallmoney'',''money'',' ELSE '' END + '''char'',''varchar'',''nchar'',''nvarchar'',''timestamp'',''uniqueidentifier''' + CASE @SearchStrInXML WHEN 1 THEN ',''xml''' ELSE '' END + ')
AND COLUMN_NAME LIKE COALESCE(' + CASE WHEN @SearchStrColumnName IS NULL THEN 'NULL' ELSE '''' + @SearchStrColumnName + '''' END + ',COLUMN_NAME)'
INSERT INTO @ColumnNameTable
EXEC (@sql)
PRINT @ColumnName
SELECT TOP 1 @ColumnName = COLUMN_NAME,@ColumnType = DATA_TYPE FROM @ColumnNameTable
SET @sql = 'SELECT ''' + @TableName + ''',''' + @ColumnName + ''',' + CASE @ColumnType WHEN 'xml' THEN 'LEFT(CAST(' + @ColumnName + ' AS nvarchar(MAX)), 4096),'''
WHEN 'timestamp' THEN 'master.dbo.fn_varbintohexstr('+ @ColumnName + '),'''
ELSE 'LEFT(' + @ColumnName + ', 4096),''' END + @ColumnType + '''
FROM ' + @TableName + ' (NOLOCK) ' +
' WHERE ' + CASE @ColumnType WHEN 'xml' THEN 'CAST(' + @ColumnName + ' AS nvarchar(MAX))'
WHEN 'timestamp' THEN 'master.dbo.fn_varbintohexstr('+ @ColumnName + ')'
ELSE @ColumnName END + ' LIKE ' + @QuotedSearchStrColumnValue
IF @@ROWCOUNT > 0 IF @FullRowResult = 1
SET @sql = 'SELECT TOP ' + CAST(@FullRowResultRows AS VARCHAR(3)) + ' ''' + @TableName + ''' AS [TableFound],''' + @ColumnName + ''' AS [ColumnFound],''FullRow>'' AS [FullRow>],*' +
' FROM ' + @TableName + ' (NOLOCK) ' +
' WHERE ' + CASE @ColumnType WHEN 'xml' THEN 'CAST(' + @ColumnName + ' AS nvarchar(MAX))'
WHEN 'timestamp' THEN 'master.dbo.fn_varbintohexstr('+ @ColumnName + ')'
ELSE @ColumnName END + ' LIKE ' + @QuotedSearchStrColumnValue
DELETE FROM @ColumnNameTable WHERE COLUMN_NAME = @ColumnName

SELECT TableName, ColumnName, ColumnValue, ColumnType, COUNT(*) AS Count FROM #Results
GROUP BY TableName, ColumnName, ColumnValue, ColumnType

Delete first character of a string in Javascript

Here's one that doesn't assume the input is a string, uses substring, and comes with a couple of unit tests:

var cutOutZero = function(value) {
    if (value.length && value.length > 0 && value[0] === '0') {
        return value.substring(1);

    return value;

Run PostgreSQL queries from the command line

I also noticed that the query

SELECT * FROM tablename;

gives an error on the psql command prompt and

SELECT * FROM "tablename";

runs fine, really strange, so don't forget the double quotes. I always liked databases :-(

Do you use NULL or 0 (zero) for pointers in C++?

I'm with Stroustrup on this one :-) Since NULL is not part of the language, I prefer to use 0.

Single selection in RecyclerView

            public class GetStudentAdapter extends 
            RecyclerView.Adapter<GetStudentAdapter.MyViewHolder> {

            private List<GetStudentModel> getStudentList;
            Context context;
            RecyclerView recyclerView;

            public class MyViewHolder extends RecyclerView.ViewHolder {
                TextView textStudentName;
                RadioButton rbSelect;

                public MyViewHolder(View view) {
                    textStudentName = (TextView) view.findViewById(;
                    rbSelect = (RadioButton) view.findViewById(;


            public GetStudentAdapter(Context context, RecyclerView recyclerView, List<GetStudentModel> getStudentList) {
                this.getStudentList = getStudentList;
                this.recyclerView = recyclerView;
                this.context = context;

            public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
                View itemView = LayoutInflater.from(parent.getContext())
                        .inflate(R.layout.select_student_list_item, parent, false);
                return new MyViewHolder(itemView);

            public void onBindViewHolder(final MyViewHolder holder, final int position) {
                holder.rbSelect.setTag(position); // This line is important.
                holder.rbSelect.setOnClickListener(onStateChangedListener(holder.rbSelect, position));


            public int getItemCount() {
                return getStudentList.size();
            private View.OnClickListener onStateChangedListener(final RadioButton checkBox, final int position) {
                return new View.OnClickListener() {
                    public void onClick(View v) {
                        if (checkBox.isChecked()) {
                            for (int i = 0; i < getStudentList.size(); i++) {



                        } else {




Replace last occurrence of character in string

Another super clear way of doing this could be as follows:

let modifiedString = originalString
   .replace('_', '')

Has been compiled by a more recent version of the Java Runtime (class file version 57.0)

I was facing same problem when I installed JRE by Oracle and solved this problem after my research.

I moved the environment path C:\Program Files (x86)\Common Files\Oracle\Java\javapath below H:\Program Files\Java\jdk-13.0.1\bin

Like this:


H:\Program Files\Java\jdk-13.0.1\bin
C:\Program Files (x86)\Common Files\Oracle\Java\javapath




how to delete all cookies of my website in php

$past = time() - 3600;
foreach ( $_COOKIE as $key => $value )
    setcookie( $key, $value, $past, '/' );

Even better is however to remember (or store it somewhere) which cookies are set with your application on a domain and delete all those directly.
That way you can be sure to delete all values correctly.

Check synchronously if file/directory exists in Node.js

updated asnwer for those people 'correctly' pointing out it doesnt directly answer the question, more bring an alternative option.

Sync solution:

fs.existsSync('filePath') also see docs here.

Returns true if the path exists, false otherwise.

Async Promise solution

In an async context you could just write the async version in sync method with using the await keyword. You can simply turn the async callback method into an promise like this:

function fileExists(path){
  return new Promise((resolve, fail) => fs.access(path, fs.constants.F_OK, 
    (err, result) => err ? fail(err) : resolve(result))
  //F_OK checks if file is visible, is default does no need to be specified.


async function doSomething() {
  var exists = await fileExists('filePath');
    console.log('file exists');

the docs on access().

Asyncio.gather vs asyncio.wait

In addition to all the previous answers, I would like to tell about the different behavior of gather() and wait() in case they are cancelled.

Gather cancellation

If gather() is cancelled, all submitted awaitables (that have not completed yet) are also cancelled.

Wait cancellation

If the wait() task is cancelled, it simply throws an CancelledError and the waited tasks remain intact.

Simple example:

import asyncio

async def task(arg):
    await asyncio.sleep(5)
    return arg

async def cancel_waiting_task(work_task, waiting_task):
    await asyncio.sleep(2)
        await waiting_task
        print("Waiting done")
    except asyncio.CancelledError:
        print("Waiting task cancelled")

        res = await work_task
        print(f"Work result: {res}")
    except asyncio.CancelledError:
        print("Work task cancelled")

async def main():
    work_task = asyncio.create_task(task("done"))
    waiting = asyncio.create_task(asyncio.wait({work_task}))
    await cancel_waiting_task(work_task, waiting)

    work_task = asyncio.create_task(task("done"))
    waiting = asyncio.gather(work_task)
    await cancel_waiting_task(work_task, waiting)


Waiting task cancelled
Work result: done
Waiting task cancelled
Work task cancelled

Sometimes it becomes necessary to combine wait() and gather() functionality. For example, we want to wait for the completion of at least one task and cancel the rest pending tasks after that, and if the waiting itself was canceled, then also cancel all pending tasks.

As real examples, let's say we have a disconnect event and a work task. And we want to wait for the results of the work task, but if the connection was lost, then cancel it. Or we will make several parallel requests, but upon completion of at least one response, cancel all others.

It could be done this way:

import asyncio
from typing import Optional, Tuple, Set

async def wait_any(
        tasks: Set[asyncio.Future], *, timeout: Optional[int] = None,
) -> Tuple[Set[asyncio.Future], Set[asyncio.Future]]:
    tasks_to_cancel: Set[asyncio.Future] = set()
        done, tasks_to_cancel = await asyncio.wait(
            tasks, timeout=timeout, return_when=asyncio.FIRST_COMPLETED
        return done, tasks_to_cancel
    except asyncio.CancelledError:
        tasks_to_cancel = tasks
        for task in tasks_to_cancel:

async def task():
    await asyncio.sleep(5)

async def cancel_waiting_task(work_task, waiting_task):
    await asyncio.sleep(2)
        await waiting_task
        print("Waiting done")
    except asyncio.CancelledError:
        print("Waiting task cancelled")

        res = await work_task
        print(f"Work result: {res}")
    except asyncio.CancelledError:
        print("Work task cancelled")

async def check_tasks(waiting_task, working_task, waiting_conn_lost_task):
        await waiting_task
        print("waiting is done")
    except asyncio.CancelledError:
        print("waiting is cancelled")

        await waiting_conn_lost_task
        print("connection is lost")
    except asyncio.CancelledError:
        print("waiting connection lost is cancelled")

        await working_task
        print("work is done")
    except asyncio.CancelledError:
        print("work is cancelled")

async def work_done_case():
    working_task = asyncio.create_task(task())
    connection_lost_event = asyncio.Event()
    waiting_conn_lost_task = asyncio.create_task(connection_lost_event.wait())
    waiting_task = asyncio.create_task(wait_any({working_task, waiting_conn_lost_task}))
    await check_tasks(waiting_task, working_task, waiting_conn_lost_task)

async def conn_lost_case():
    working_task = asyncio.create_task(task())
    connection_lost_event = asyncio.Event()
    waiting_conn_lost_task = asyncio.create_task(connection_lost_event.wait())
    waiting_task = asyncio.create_task(wait_any({working_task, waiting_conn_lost_task}))
    await asyncio.sleep(2)
    connection_lost_event.set()  # <---
    await check_tasks(waiting_task, working_task, waiting_conn_lost_task)

async def cancel_waiting_case():
    working_task = asyncio.create_task(task())
    connection_lost_event = asyncio.Event()
    waiting_conn_lost_task = asyncio.create_task(connection_lost_event.wait())
    waiting_task = asyncio.create_task(wait_any({working_task, waiting_conn_lost_task}))
    await asyncio.sleep(2)
    waiting_task.cancel()  # <---
    await check_tasks(waiting_task, working_task, waiting_conn_lost_task)

async def main():
    print("Work done")
    await work_done_case()
    print("\nConnection lost")
    await conn_lost_case()
    print("\nCancel waiting")
    await cancel_waiting_case()


Work done
waiting is done
waiting connection lost is cancelled
work is done

Connection lost
waiting is done
connection is lost
work is cancelled

Cancel waiting
waiting is cancelled
waiting connection lost is cancelled
work is cancelled

"Server Tomcat v7.0 Server at localhost failed to start" without stack trace while it works in terminal

  1. Open the Servers Tab from Windows ? Show View ? Servers menu

  2. Right click on the server and delete it

  3. Create a new server by going New ? Server on Server Tab

  4. Click on "Configure runtime environments…" link

  5. Select the Apache Tomcat v7.0 server and remove it. This will remove the Tomcat server configuration. This is where many people do mistake – they remove the server but do not remove the Runtime environment.

  6. Click on OK and exit the screen above now.

  7. From the screen below, choose Apache Tomcat v7.0 server and click on next button.

  8. Browse to Tomcat Installation Directory

  9. Click on Next and choose which project you would like to deploy:

  10. Click on Finish after Adding your project

  11. Now launch your server. This will fix your Server timeout or any issues with old server configuration. This solution can also be used to fix “port update not being taking place” issues.

Global keyboard capture in C# application

My rep is too low to comment, but concerning the CallbackOnCollectedDelegate exception, I modified the public void SetupKeyboardHooks() in C4d's answer to look like this:

public void SetupKeyboardHooks(out object hookProc)
  _globalKeyboardHook = new GlobalKeyboardHook();
  _globalKeyboardHook.KeyboardPressed += OnKeyPressed;

  hookProc = _globalKeyboardHook.GcSafeHookProc;

where GcSafeHookProc is just a public getter for _hookProc in OPs

_hookProc = LowLevelKeyboardProc; // we must keep alive _hookProc, because GC is not aware about SetWindowsHookEx behaviour.

and stored the hookProc as a private field in the class calling the SetupKeyboardHooks(...), therefore keeping the reference alive, save from garbage collection, no more CallbackOnCollectedDelegate exception. Seems having this additional reference in the GlobalKeyboardHook class is not sufficient. Maybe make sure that this reference is also disposed when closing your app.

How to kill/stop a long SQL query immediately?

apparently on sql server 2008 r2 64bit, with long running query from IIS the kill spid doesn't seem to work, the query just gets restarted again and again. and it seems to be reusing the spid's. the query is causing sql server to take like 35% cpu constantly and hang the website. I'm guessing bc/ it can't respond to other queries for logging in

How to print a int64_t type in C

//VC6.0 (386 & better)

    __int64 my_qw_var = 0x1234567890abcdef;

    __int32 v_dw_h;
    __int32 v_dw_l;

            mov eax,[dword ptr my_qw_var + 4]   //dwh
            mov [dword ptr v_dw_h],eax

            mov eax,[dword ptr my_qw_var]   //dwl
            mov [dword ptr v_dw_l],eax

        //Oops 0.8 format
    printf("val = 0x%0.8x%0.8x\n", (__int32)v_dw_h, (__int32)v_dw_l);


scale fit mobile web content using viewport meta tag

Try adding a style="width:100%;" to the img tag. That way the image will fill up the entire width of the page, thus scaling down if the image is larger than the viewport.

What is the difference between pull and clone in git?

They're basically the same, except clone will setup additional remote tracking branches, not just master. Check out the man page:

Clones a repository into a newly created directory, creates remote-tracking branches for each branch in the cloned repository (visible using git branch -r), and creates and checks out an initial branch that is forked from the cloned repository's currently active branch.

Converting newline formatting from Mac to Windows

The following is a complete script based on the above answers along with sanity checking and works on Mac OS X and should work on other Linux / Unix systems as well (although this has not been tested).



# =============================================================================
# =
# =
# =
# = MODE is one of unix2dos, dos2unix, tounix, todos, tomac
# = FILENAME is modified in-place
# = If SCRIPT is one of the modes (with or without .sh extension), then MODE
# =   can be omitted - it is inferred from the script name.
# = The script does use the file command to test if it is a text file or not,
# =   but this is not a guarantee.
# =
# =============================================================================

modes="unix2dos dos2unix todos tounix tomac"

usage() {
    echo "USAGE:  $script [ mode ] filename"
    echo "MODE is one of:"
    echo $modes
    echo "NOTE:  The tomac mode is intended for old Mac OS versions and should not be"
    echo "used without good reason."
    echo "The file is modified in-place so there is no output filename."
    echo "USE AT YOUR OWN RISK."
    echo "The script does try to check if it's a binary or text file for sanity, but"
    echo "this is not guaranteed."
    echo "Symbolic links to this script may use the above names and be recognized as"
    echo "mode operators."
    echo "Press RETURN to exit."
    read answer

# -- Look for the mode as the scriptname
mode="`basename "$0" .sh`"

# -- If 2 arguments use as mode and filename
if [ ! -z "$2" ] ; then mode="$1"; fname="$2"; fi

# -- Check there are 1 or 2 arguments or print usage.
if [ ! -z "$3" -o -z "$1" ] ; then usage; fi

# -- Check if the mode found is valid.
for checkmode in $modes; do if [ $mode = $checkmode ] ; then validmode=yes; fi; done
# -- If not a valid mode, abort.
if [ $validmode = no ] ; then echo Invalid mode $mode...aborting.; echo; usage; fi

# -- If the file doesn't exist, abort.
if [ ! -e "$fname" ] ; then echo Input file $fname does not exist...aborting.; echo; usage; fi

# -- If the OS thinks it's a binary file, abort, displaying file information.
if [ -z "`file "$fname" | grep text`" ] ; then echo Input file $fname may be a binary file...aborting.; echo; file "$fname"; echo; usage; fi

# -- Do the in-place conversion.
case "$mode" in
#   unix2dos ) # sed does not behave on Mac - replace w/ "todos" and "tounix"
#       # Plus, these variants are more universal and assume less.
#       sed -e 's/$/\r/' -i '' "$fname"             # UNIX to DOS  (adding CRs)
#       ;;
#   dos2unix )
#       sed -e 's/\r$//' -i '' "$fname"             # DOS  to UNIX (removing CRs)
#           ;;
    "unix2dos" | "todos" )
        perl -pi -e 's/\r\n|\n|\r/\r\n/g' "$fname"  # Convert to DOS
    "dos2unix" | "tounix" )
        perl -pi -e 's/\r\n|\n|\r/\n/g'   "$fname"  # Convert to UNIX
    "tomac" )
        perl -pi -e 's/\r\n|\n|\r/\r/g'   "$fname"  # Convert to old Mac
    * ) # -- Not strictly needed since mode is checked first.
        echo Invalid mode $mode...aborting.; echo; usage

# -- Display result.
if [ "$?" = "0" ] ; then echo "File $fname updated with mode $mode."; else echo "Conversion failed return code $?."; echo; usage; fi

How can I know if Object is String type object?

Could you not use typeof(object) to compare against

The name 'controlname' does not exist in the current context

Also, make sure you have no files that accidentally try to inherit or define the same (partial) class as other files. Note that these files can seem unrelated to the files where the error actually appeared!

How to do URL decoding in Java?

%3A and %2F are URL encoded characters. Use this java code to convert them back into : and /

String decoded =, "UTF-8");

How do you cast a List of supertypes to a List of subtypes?

The problem is that your method does NOT return a list of TestA if it contains a TestB, so what if it was correctly typed? Then this cast:

class TestA{};
class TestB extends TestA{};
List<? extends TestA> listA;
List<TestB> listB = (List<TestB>) listA;

works about as well as you could hope for (Eclipse warns you of an unchecked cast which is exactly what you are doing, so meh). So can you use this to solve your problem? Actually you can because of this:

List<TestA> badlist = null; // Actually contains TestBs, as specified
List<? extends TestA> talist = badlist;  // Umm, works
List<TextB> tblist = (List<TestB>)talist; // TADA!

Exactly what you asked for, right? or to be really exact:

List<TestB> tblist = (List<TestB>)(List<? extends TestA>) badlist;

seems to compile just fine for me.

How to change scroll bar position with CSS?

Try this out. Hope this helps

<div id="single" dir="rtl">
    <div class="common">Single</div>

<div id="both" dir="ltr">
    <div class="common">Both</div>

#single, #both{
    width: 100px;
    height: 100px;
    overflow: auto;
    margin: 0 auto;
    border: 1px solid gray;

    height: 150px;
    width: 150px;

Hosting ASP.NET in IIS7 gives Access is denied?

This is what happened to me:

Get - Post is ok. Working well.

When I try to use Options verb, the server return error like that.


Then, beware with urlScan

I add OPTIONS verb to urlscan configuration .ini file, then everything works well.

To check if urlscan is installed or not, open your iis manager, and open ISAPI FILTERS url scan should appear at the list.

How to show Error & Warning Message Box in .NET/ How to Customize MessageBox

  "your message",
  "window title", 
  MessageBoxIcon.Asterisk //For Info Asterisk
  MessageBoxIcon.Exclamation //For triangle Warning 

Getting all names in an enum as a String[]

With java 8:

Import SQL dump into PostgreSQL database

I use:

cat /home/path/to/dump/file | psql -h localhost -U <user_name> -d <db_name>

Hope this will help someone.

How to get the element clicked (for the whole document)?

$(document).click(function (e) {

How to count items in JSON object using command line?

The shortest expression is

curl 'http://…' | jq length

How to maximize the browser window in Selenium WebDriver (Selenium 2) using C#?

We have observed bug with new driver libraries. You can use slightly old jars which are able to handle new browsers versions.

The main generic option is :-


You can also use other option for maximizing the browser window.


Add below option and pass it to driver:-


The full code will look like below :-

ChromeOptions chromeOptions = new ChromeOptions();
driver = new ChromeDriver(chromeOptions);


Toolkit toolkit = Toolkit.getDefaultToolkit();
int Width = (int) toolkit.getScreenSize().getWidth();
int Height = (int)toolkit.getScreenSize().getHeight();
//For Dimension class, Import following library "org.openqa.selenium.Dimension"  
driver.manage().window().setSize(new Dimension(Width,Height));

Try this on safari :-

JavascriptExecutor jse = (JavascriptExecutor)driver;
String screenWidth = jse.executeScript("return screen.availWidth").toString();
String screenHeight = jse.executeScript("return screen.availHeight").toString();
int intScreenWidth = Integer.parseInt(screenWidth);
int intScreenHeight = Integer.parseInt(screenHeight);
Dimension d = new Dimension(intScreenWidth, intScreenHeight);

Define preprocessor macro through CMake?

For a long time, CMake had the add_definitions command for this purpose. However, recently the command has been superseded by a more fine grained approach (separate commands for compile definitions, include directories, and compiler options).

An example using the new add_compile_definitions:



add_compile_definitions(OPENCV_VERSION=${OpenCV_VERSION} WITH_OPENCV2)

The good part about this is that it circumvents the shabby trickery CMake has in place for add_definitions. CMake is such a shabby system, but they are finally finding some sanity.

Find more explanation on which commands to use for compiler flags here:

Likewise, you can do this per-target as explained in Jim Hunziker's answer.

Get file version in PowerShell

This is based on the other answers, but is exactly what I was after:

(Get-Command C:\Path\YourFile.Dll).FileVersionInfo.FileVersion

Converting PHP result array to JSON

json_encode is available in php > 5.2.0:


Loop over html table and get checked checkboxes (JQuery)

The following code snippet enables/disables a button depending on whether at least one checkbox on the page has been checked.
$('input[type=checkbox]').change(function () {
    $('#test > tbody  tr').each(function () {
        if ($('input[type=checkbox]').is(':checked')) {
        } else {
            $('#btnexcellSelect').attr('disabled', 'disabled');
        if ($(this).is(':checked')){
            console.log( $(this).attr('id'));

Here is demo in JSFiddle.

Transfer files to/from session I'm logged in with PuTTY

There's no way to initiate a file transfer back to/from local Windows from a SSH session opened in PuTTY window.

Though PuTTY supports connection-sharing.

While you still need to run a compatible file transfer client (the pscp or psftp), no new login is required, it automatically (if enabled) makes use of an existing PuTTY session.

To enable the sharing see:
Sharing an SSH connection between PuTTY tools.

Alternative way is to use WinSCP, a GUI SFTP/SCP client. While you browse the remote site, you can anytime open SSH terminal to the same site using Open in PuTTY button.

See Opening Session in PuTTY.

With an additional setup, you can even make PuTTY automatically navigate to the same directory you are browsing with WinSCP.

See Opening PuTTY in the Same Directory.

(I'm the author of WinSCP)

How to convert an NSString into an NSNumber

Here's a working sample of NSNumberFormatter reading localized number NSString (xCode 3.2.4, osX 10.6), to save others the hours I've just spent messing around. Beware: while it can handle trailing blanks ("8,765.4 " works), this cannot handle leading white space and this cannot handle stray text characters. (Bad input strings: " 8" and "8q" and "8 q".)

NSString *tempStr = @"8,765.4";  
     // localization allows other thousands separators, also.
NSNumberFormatter * myNumFormatter = [[NSNumberFormatter alloc] init];
[myNumFormatter setLocale:[NSLocale currentLocale]]; // happen by default?
[myNumFormatter setFormatterBehavior:NSNumberFormatterBehavior10_4];
     // next line is very important!
[myNumFormatter setNumberStyle:NSNumberFormatterDecimalStyle]; // crucial

NSNumber *tempNum = [myNumFormatter numberFromString:tempStr];
NSLog(@"string '%@' gives NSNumber '%@' with intValue '%i'", 
    tempStr, tempNum, [tempNum intValue]);
[myNumFormatter release];  // good citizen

What does "javax.naming.NoInitialContextException" mean?

It means that there is no initial context :)

But seriously folks, JNDI (javax.naming) is all about looking up objects or resources from some directory or provider. To look something up, you need somewhere to look (this is the InitialContext). NoInitialContextException means "I want to find the telephone number for John Smith, but I have no phonebook to look in".

An InitialContext can be created in any number of ways. It can be done manually, for instance creating a connection to an LDAP server. It can also be set up by an application server inside which you run your application. In this case, the container (application server) already provides you with a "phonebook", through which you can look up anything the application server makes available. This is often configurable and a common way of moving this type of configuration from the application implementation to the container, where it can be shared across all applications in the server.

UPDATE: from the code snippet you post it looks like you are trying to run code stand-alone that is meant to be run in an application server. In this case, the code attempting to get a connection to a database from the "phonebook". This is one of the resources that is often configured in the application server container. So, rather than having to manage configuration and connections to the database in your code, you can configure it in your application server and simple ask for a connection (using JNDI) in your code.

Blank HTML SELECT without blank item in dropdown list

You can by setting selectedIndex to -1 using .prop:

For older jQuery versions use .attr instead of .prop:

Java IOException "Too many open files"

Although in most general cases the error is quite clearly that file handles have not been closed, I just encountered an instance with JDK7 on Linux that well... is sufficiently ****ed up to explain here.

The program opened a FileOutputStream (fos), a BufferedOutputStream (bos) and a DataOutputStream (dos). After writing to the dataoutputstream, the dos was closed and I thought everything went fine.

Internally however, the dos, tried to flush the bos, which returned a Disk Full error. That exception was eaten by the DataOutputStream, and as a consequence the underlying bos was not closed, hence the fos was still open.

At a later stage that file was then renamed from (something with a .tmp) to its real name. Thereby, the java file descriptor trackers lost track of the original .tmp, yet it was still open !

To solve this, I had to first flush the DataOutputStream myself, retrieve the IOException and close the FileOutputStream myself.

I hope this helps someone.

Vector of Vectors to create matrix

You have to initialize the vector of vectors to the appropriate size before accessing any elements. You can do it like this:

// assumes using std::vector for brevity
vector<vector<int>> matrix(RR, vector<int>(CC));

This creates a vector of RR size CC vectors, filled with 0.

How to use Git Revert

The question is quite old but revert is still confusing people (like me)

As a beginner, after some trial and error (more errors than trials) I've got an important point:

  • git revert requires the id of the commit you want to remove keeping it into your history

  • git reset requires the commit you want to keep, and will consequentially remove anything after that from history.

That is, if you use revert with the first commit id, you'll find yourself into an empty directory and an additional commit in history, while with reset your directory will be.. reverted back to the initial commit and your history will get as if the last commit(s) never happened.

To be even more clear, with a log like this:

# git log --oneline

cb76ee4 wrong
01b56c6 test
2e407ce first commit

Using git revert cb76ee4 will by default bring your files back to 01b56c6 and will add a further commit to your history:

8d4406b Revert "wrong"
cb76ee4 wrong
01b56c6 test
2e407ce first commit

git reset 01b56c6 will instead bring your files back to 01b56c6 and will clean up any other commit after that from your history :

01b56c6 test
2e407ce first commit

I know these are "the basis" but it was quite confusing for me, by running revert on first id ('first commit') I was expecting to find my initial files, it taken a while to understand, that if you need your files back as 'first commit' you need to use the next id.

How to execute a Python script from the Django shell?

The << part is wrong, use < instead:

$ ./ shell <

You could also do:

$ ./ shell
>>> execfile('')

For python3 you would need to use

>>> exec(open('').read())

HTML button onclick event

Try this:-

<!DOCTYPE html> 
    <meta charset="ISO-8859-1"> 
    <title>Online Student Portal</title> 
    <form action="">
         <input type="button" value="Add Students" onclick="window.location.href='Students.html';"/>
         <input type="button" value="Add Courses" onclick="window.location.href='Courses.html';"/>
         <input type="button" value="Student Payments" onclick="window.location.href='Payment.html';"/>

Google Chrome forcing download of "f.txt" file

Seems related to!msg/google-caja-discuss/ite6K5c8mqs/Ayqw72XJ9G8J.

The so-called "Rosetta Flash" vulnerability is that allowing arbitrary yet identifier-like text at the beginning of a JSONP response is sufficient for it to be interpreted as a Flash file executing in that origin. See for more information:

JSONP responses from the proxy servlet now: * are prefixed with "/**/", which still allows them to execute as JSONP but removes requester control over the first bytes of the response. * have the response header Content-Disposition: attachment.

Html table with button on each row

Pretty sure this solves what you're looking for:


    <tr><td><button class="editbtn">edit</button></td></tr>
    <tr><td><button class="editbtn">edit</button></td></tr>
    <tr><td><button class="editbtn">edit</button></td></tr>
    <tr><td><button class="editbtn">edit</button></td></tr>

Javascript (using jQuery):

        $(this).html($(this).html() == 'edit' ? 'modify' : 'edit');


Apparently I should have looked at your sample code first ;)

You need to change (at least) the ID attribute of each element. The ID is the unique identifier for each element on the page, meaning that if you have multiple items with the same ID, you'll get conflicts.

By using classes, you can apply the same logic to multiple elements without any conflicts.

JSFiddle sample

rotating axis labels in R

Not sure if this is what you mean, but try setting las=1. Here's an example:

tN <- table(Ni <- stats::rpois(100, lambda=5))
r <- barplot(tN, col=rainbow(20), las=1)


That represents the style of axis labels. (0=parallel, 1=all horizontal, 2=all perpendicular to axis, 3=all vertical)

How much overhead does SSL impose?

Assuming you don't count connection set-up (as you indicated in your update), it strongly depends on the cipher chosen. Network overhead (in terms of bandwidth) will be negligible. CPU overhead will be dominated by cryptography. On my mobile Core i5, I can encrypt around 250 MB per second with RC4 on a single core. (RC4 is what you should choose for maximum performance.) AES is slower, providing "only" around 50 MB/s. So, if you choose correct ciphers, you won't manage to keep a single current core busy with the crypto overhead even if you have a fully utilized 1 Gbit line. [Edit: RC4 should not be used because it is no longer secure. However, AES hardware support is now present in many CPUs, which makes AES encryption really fast on such platforms.]

Connection establishment, however, is different. Depending on the implementation (e.g. support for TLS false start), it will add round-trips, which can cause noticable delays. Additionally, expensive crypto takes place on the first connection establishment (above-mentioned CPU could only accept 14 connections per core per second if you foolishly used 4096-bit keys and 100 if you use 2048-bit keys). On subsequent connections, previous sessions are often reused, avoiding the expensive crypto.

So, to summarize:

Transfer on established connection:

  • Delay: nearly none
  • CPU: negligible
  • Bandwidth: negligible

First connection establishment:

  • Delay: additional round-trips
  • Bandwidth: several kilobytes (certificates)
  • CPU on client: medium
  • CPU on server: high

Subsequent connection establishments:

  • Delay: additional round-trip (not sure if one or multiple, may be implementation-dependant)
  • Bandwidth: negligible
  • CPU: nearly none

How do you configure HttpOnly cookies in tomcat / java webapps?

If your web server supports Serlvet 3.0 spec, like tomcat 7.0+, you can use below in web.xml as:


As mentioned in docs:

HttpOnly: Specifies whether any session tracking cookies created by this web application will be marked as HttpOnly

Secure: Specifies whether any session tracking cookies created by this web application will be marked as secure even if the request that initiated the corresponding session is using plain HTTP instead of HTTPS

Please refer to how to set httponly and session cookie for java web application

Converting NSString to NSDictionary / JSON

Use the following code to get the response object from the AFHTTPSessionManager failure block; then you can convert the generic type into the required data type:

id responseObject = [NSJSONSerialization JSONObjectWithData:(NSData *)error.userInfo[AFNetworkingOperationFailingURLResponseDataErrorKey] options:0 error:nil];

How to do multiline shell script in Ansible

Ansible uses YAML syntax in its playbooks. YAML has a number of block operators:

  • The > is a folding block operator. That is, it joins multiple lines together by spaces. The following syntax:

    key: >
      This text
      has multiple

    Would assign the value This text has multiple lines\n to key.

  • The | character is a literal block operator. This is probably what you want for multi-line shell scripts. The following syntax:

    key: |
      This text
      has multiple

    Would assign the value This text\nhas multiple\nlines\n to key.

You can use this for multiline shell scripts like this:

- name: iterate user groups
  shell: |
    groupmod -o -g {{ item['guid'] }} {{ item['username'] }} 
  with_items: "{{ users }}"

There is one caveat: Ansible does some janky manipulation of arguments to the shell command, so while the above will generally work as expected, the following won't:

- shell: |
    cat <<EOF
    This is a test.

Ansible will actually render that text with leading spaces, which means the shell will never find the string EOF at the beginning of a line. You can avoid Ansible's unhelpful heuristics by using the cmd parameter like this:

- shell:
    cmd: |
      cat <<EOF
      This is a test.

Correct way to write line to file?

Since 3.5 you can also use the pathlib for that purpose:

Path.write_text(data, encoding=None, errors=None)

Open the file pointed to in text mode, write data to it, and close the file:

import pathlib


How do I disable right click on my web page?

Just do this


<body oncontextmenu="return false">

Making an array of integers in iOS

If the order of your integers is not required, and if there are only unique values

you can also use NSIndexSet or NSMutableIndexSet You will be able to easily add and remove integers, or check if your array contains an integer with

- (void)addIndex:(NSUInteger)index
- (void)removeIndex:(NSUInteger)index
- (BOOL)containsIndexes:(NSIndexSet *)indexSet

Check the documentation for more info.

Angular-Material DateTime Picker Component?

Unfortunately, the answer to your question of whether there is official Material support for selecting the time is "No", but it's currently an open issue on the official Material2 GitHub repo:

Hopefully this changes soon, in the mean time, you'll have to fight with the 3rd-party ones you've already discovered. There are a few people in that GitHub issue that provide their self-made workarounds that you can try.

Modulo operation with negative numbers

C99 requires that when a/b is representable:

(a/b) * b + a%b shall equal a

This makes sense, logically. Right?

Let's see what this leads to:

Example A. 5/(-3) is -1

=> (-1) * (-3) + 5%(-3) = 5

This can only happen if 5%(-3) is 2.

Example B. (-5)/3 is -1

=> (-1) * 3 + (-5)%3 = -5

This can only happen if (-5)%3 is -2

FB OpenGraph og:image not pulling images (possibly https?)

In my case the problem was in not providing CA Root Certificate. I figured it out after using: to analyze SSL configuration.

How to target the href to div

You can put all your #m1...#m9 divs into .target and display them based on fragment identifier (hash) using :target pseudo-class. It doesn't move the contents between divs, but I think the effect is close to what you wanted to achieve.



<div class="target">
    <div id="m1">
        dasdasdasd m1
    <!-- etc... -->
    <div id="m9">
        dasdasdsgaswa m9


.target {
    border:solid black 1px; 
.target > div {

.target > div:target{

Download large file in python with requests

Not exactly what OP was asking, but... it's ridiculously easy to do that with urllib:

from urllib.request import urlretrieve
url = ''
dst = 'ubuntu-16.04.2-desktop-amd64.iso'
urlretrieve(url, dst)

Or this way, if you want to save it to a temporary file:

from urllib.request import urlopen
from shutil import copyfileobj
from tempfile import NamedTemporaryFile
url = ''
with urlopen(url) as fsrc, NamedTemporaryFile(delete=False) as fdst:
    copyfileobj(fsrc, fdst)

I watched the process:

watch 'ps -p 18647 -o pid,ppid,pmem,rsz,vsz,comm,args; ls -al *.iso'

And I saw the file growing, but memory usage stayed at 17 MB. Am I missing something?

How do I size a UITextView to its content?

To make a dynamically sizing UITextView inside a UITableViewCell, I found the following combination works in Xcode 6 with the iOS 8 SDK:

  • Add a UITextView to a UITableViewCell and constrain it to the sides
  • Set the UITextView's scrollEnabled property to NO. With scrolling enabled, the frame of the UITextView is independent of its content size, but with scrolling disabled, there is a relationship between the two.
  • If your table is using the original default row height of 44 then it will automatically calculate row heights, but if you changed the default row height to something else, you may need to manually switch on auto-calculation of row heights in viewDidLoad:

    tableView.estimatedRowHeight = 150;
    tableView.rowHeight = UITableViewAutomaticDimension;

For read-only dynamically sizing UITextViews, that’s it. If you’re allowing users to edit the text in your UITextView, you also need to:

  • Implement the textViewDidChange: method of the UITextViewDelegate protocol, and tell the tableView to repaint itself every time the text is edited:

    - (void)textViewDidChange:(UITextView *)textView;
        [tableView beginUpdates];
        [tableView endUpdates];
  • And don’t forget to set the UITextView delegate somewhere, either in Storyboard or in tableView:cellForRowAtIndexPath:

How to compare only date in moment.js

For checking one date is after another by using isAfter() method.

moment('2020-01-20').isAfter('2020-01-21'); // false
moment('2020-01-20').isAfter('2020-01-19'); // true

For checking one date is before another by using isBefore() method.

moment('2020-01-20').isBefore('2020-01-21'); // true
moment('2020-01-20').isBefore('2020-01-19'); // false

For checking one date is same as another by using isSame() method.

moment('2020-01-20').isSame('2020-01-21'); // false
moment('2020-01-20').isSame('2020-01-20'); // true

PHP: How do you determine every Nth iteration of a loop?

Going off of @Powerlord's answer,

"There is one catch: 0 % 3 is equal to 0. This could result in unexpected results if your counter starts at 0."

You can still start your counter at 0 (arrays, querys), but offset it

if (($counter + 1) % 3 == 0) {
  echo 'image file';

Hide keyboard in react-native

Updated usage of ScrollView for React Native 0.39

<ScrollView scrollEnabled={false} contentContainerStyle={{flex: 1}} />

Although, there is still a problem with two TextInput boxes. eg. A username and password form would now dismiss the keyboard when switching between inputs. Would love to get some suggestions to keep keyboard alive when switching between TextInputs while using a ScrollView.

Laravel: Validation unique on update

an even simpler solution tested with version 5.2

in your model

// validator rules
public static $rules = array(
    'email_address' => 'email|required|unique:users,id'

How to show alert message in mvc 4 controller?

Use this:

return JavaScript(alert("Hello this is an alert"));


return Content("<script language='javascript' type='text/javascript'>alert('Thanks for Feedback!');</script>");

How to read strings from a Scanner in a Java console application?

You are entering a null value to nextInt, it will fail if you give a null value...

i have added a null check to the piece of code

Try this code:

import java.util.Scanner;
class MyClass
     public static void main(String args[]){

                Scanner scanner = new Scanner(;
                int eid,sid;
                String ename;
                System.out.println("Enter Employeeid:");
                System.out.println("Enter EmployeeName:");
                System.out.println("Enter SupervisiorId:");
                    if(scanner.nextLine()!=null&&scanner.nextLine()!=""){//null check
                     }//null check

How to make div occupy remaining height?

I faced the same challenge myself and found these 2 answers using flex properties.


.container {
  display: flex;
  flex-direction: column;

  flex: 1;

trim left characters in sql server?

use "LEFT"

 select left('Hello World', 5)

or use "SUBSTRING"

 select substring('Hello World', 1, 5)

How do you Sort a DataTable given column and direction?

If you've only got one DataView, you can sort using that instead:

table.DefaultView.Sort = "columnName asc";

Haven't tried it, but I guess you can do this with any number of DataViews, as long as you reference the right one.

How to uncompress a tar.gz in another directory

Extracts myArchive.tar to /destinationDirectory


cd /destinationDirectory
pax -rv -f myArchive.tar -s ',^/,,'

remote rejected master -> master (pre-receive hook declined)

Check the following

  1. Make sure you add all the files and directories needed to be tracked are added using git status [You have done this]

    $ git status

  2. If not added then add them using **git add . ** [You have done this]

    $ git add .

  3. Bundle all gems and you will have Gemfile.lock

    $ bundle install
    $ git add Gemfile.lock
    $ git commit -am "Added Gemfile.lock"

  4. Push it to heroku

$ git push heroku master

Your push should work

CSS3 transitions inside jQuery .css()

Step 1) Remove the semi-colon, it's an object you're creating...

    left       : c,
    transition : 'opacity 1s ease-in-out';


    left       : c,
    transition : 'opacity 1s ease-in-out'

Step 2) Vendor-prefixes... no browsers use transition since it's the standard and this is an experimental feature even in the latest browsers:

    left             : c,
    WebkitTransition : 'opacity 1s ease-in-out',
    MozTransition    : 'opacity 1s ease-in-out',
    MsTransition     : 'opacity 1s ease-in-out',
    OTransition      : 'opacity 1s ease-in-out',
    transition       : 'opacity 1s ease-in-out'

Here is a demo:

Step 3) Better vendor-prefixes... Instead of adding tons of unnecessary CSS to elements (that will just be ignored by the browser) you can use jQuery to decide what vendor-prefix to use:

$('a').on('click', function () {
    var myTransition = ($.browser.webkit)  ? '-webkit-transition' :
                       ($.browser.mozilla) ? '-moz-transition' : 
                       ($.browser.msie)    ? '-ms-transition' :
                       ($.browser.opera)   ? '-o-transition' : 'transition',
        myCSSObj     = { opacity : 1 };

    myCSSObj[myTransition] = 'opacity 1s ease-in-out';

Here is a demo:

Also note that if you specify in your transition declaration that the property to animate is opacity, setting a left property won't be animated.

How to create the branch from specific commit in different branch

You have the arguments in the wrong order:

git branch <branch-name> <commit>

and for that, it doesn't matter what branch is checked out; it'll do what you say. (If you omit the commit argument, it defaults to creating a branch at the same place as the current one.)

If you want to check out the new branch as you create it:

git checkout -b <branch> <commit>

with the same behavior if you omit the commit argument.

Write a formula in an Excel Cell using VBA

I don't know why, but if you use

(...)Formula = "=SUM(D2,E2)"

(',' instead of ';'), it works.

If you step through your sub in the VB script editor (F8), you can add Range("F2").Formula to the watch window and see what the formular looks like from a VB point of view. It seems that the formular shown in Excel itself is sometimes different from the formular that VB sees...

Auto-increment primary key in SQL tables

I don't have Express Management Studio on this machine, so I'm going based on memory. I think you need to set the column as "IDENTITY", and there should be a [+] under properties where you can expand, and set auto-increment to true.

What is the suggested way to install brew, node.js, io.js, nvm, npm on OS X?

For install with zsh and Homebrew:

brew install nvm

Then Add the following to ~/.zshrc or your desired shell configuration file:

export NVM_DIR="$HOME/.nvm"
. "/usr/local/opt/nvm/"

Then install a node version and use it.

nvm install 7.10.1
nvm use 7.10.1

Error: "dictionary update sequence element #0 has length 1; 2 is required" on Django 1.4

You are sending one parameter incorrectly; it should be a dictionary object:

  • Wrong: func(a=r)

  • Correct: func(a={'x':y})

FFmpeg: How to split video efficiently?

The ffmpeg wiki links back to this page in reference to "How to split video efficiently". I'm not convinced this page answers that question, so I did as @AlcubierreDrive suggested…

echo "Two commands" 
time ffmpeg -v quiet -y -i input.ts -vcodec copy -acodec copy -ss 00:00:00 -t 00:30:00 -sn test1.mkv
time ffmpeg -v quiet -y -i input.ts -vcodec copy -acodec copy -ss 00:30:00 -t 01:00:00 -sn test2.mkv
echo "One command" 
time ffmpeg -v quiet -y -i input.ts -vcodec copy -acodec copy -ss 00:00:00 -t 00:30:00 \
  -sn test3.mkv -vcodec copy -acodec copy -ss 00:30:00 -t 01:00:00 -sn test4.mkv

Which outputs...

Two commands
real    0m16.201s
user    0m1.830s
sys 0m1.301s

real    0m43.621s
user    0m4.943s
sys 0m2.908s

One command
real    0m59.410s
user    0m5.577s
sys 0m3.939s

I tested a SD & HD file, after a few runs & a little maths.

Two commands SD 0m53.94 #2 wins  
One command  SD 0m49.63  

Two commands SD 0m55.00  
One command  SD 0m52.26 #1 wins 

Two commands SD 0m58.60 #2 wins  
One command  SD 0m58.61 

Two commands SD 0m54.60  
One command  SD 0m50.51 #1 wins 

Two commands SD 0m53.94  
One command  SD 0m49.63 #1 wins  

Two commands SD 0m55.00  
One command  SD 0m52.26 #1 wins 

Two commands SD 0m58.71  
One command  SD 0m58.61 #1 wins

Two commands SD 0m54.63  
One command  SD 0m50.51 #1 wins  

Two commands SD 1m6.67s #2 wins  
One command  SD 1m20.18  

Two commands SD 1m7.67  
One command  SD 1m6.72 #1 wins

Two commands SD 1m4.92  
One command  SD 1m2.24 #1 wins

Two commands SD 1m1.73  
One command  SD 0m59.72 #1 wins

Two commands HD 4m23.20  
One command  HD 3m40.02 #1 wins

Two commands SD 1m1.30  
One command  SD 0m59.59 #1 wins  

Two commands HD 3m47.89  
One command  HD 3m29.59 #1 wins  

Two commands SD 0m59.82  
One command  SD 0m59.41 #1 wins  

Two commands HD 3m51.18  
One command  HD 3m30.79 #1 wins  

SD file = 1.35GB DVB transport stream
HD file = 3.14GB DVB transport stream


The single command is better if you are handling HD, it agrees with the manuals comments on using -ss after the input file to do a 'slow seek'. SD files have a negligible difference.

The two command version should be quicker by adding another -ss before the input file for the a 'fast seek' followed by the more accurate slow seek.

How to check if array is not empty?

I can't comment yet, but it should be mentioned that if you use numpy array with more than one element this will fail:

if l:
    print "list has items"

elif not l:
    print "list is empty"

the error will be:

ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()

What is the difference between __str__ and __repr__?

__str__ can be invoked on an object by calling str(obj) and should return a human readable string.

__repr__ can be invoked on an object by calling repr(obj) and should return internal object (object fields/attributes)

This example may help:

class C1:pass

class C2:        
    def __str__(self):
        return str(f"{self.__class__.__name__} class str ")

class C3:        
    def __repr__(self):        
         return str(f"{self.__class__.__name__} class repr")

class C4:        
    def __str__(self):
        return str(f"{self.__class__.__name__} class str ")
    def __repr__(self):        
         return str(f"{self.__class__.__name__} class repr")

ci1 = C1()    
ci2 = C2()  
ci3 = C3()  
ci4 = C4()

print(ci1)       #<__main__.C1 object at 0x0000024C44A80C18>
print(str(ci1))  #<__main__.C1 object at 0x0000024C44A80C18>
print(repr(ci1)) #<__main__.C1 object at 0x0000024C44A80C18>
print(ci2)       #C2 class str
print(str(ci2))  #C2 class str
print(repr(ci2)) #<__main__.C2 object at 0x0000024C44AE12E8>
print(ci3)       #C3 class repr
print(str(ci3))  #C3 class repr
print(repr(ci3)) #C3 class repr
print(ci4)       #C4 class str 
print(str(ci4))  #C4 class str 
print(repr(ci4)) #C4 class repr

How can I conditionally import an ES6 module?

Look at this example for clear understanding of how dynamic import works.

Dynamic Module Imports Example

To have Basic Understanding of importing and exporting Modules.

JavaScript modules Github

Javascript Modules MDN

Python regex to match dates

As the question title asks for a regex that finds many dates, I would like to propose a new solution, although there are many solutions already.

In order to find all dates of a string that are in this millennium (2000 - 2999), for me it worked the following:

dates = re.findall('([1-9]|1[0-9]|2[0-9]|3[0-1]|0[0-9])(.|-|\/)([1-9]|1[0-2]|0[0-9])(.|-|\/)(20[0-9][0-9])',dates_ele)

dates = [''.join(dates[i]) for i in range(len(dates))]

This regex is able to find multiple dates in the same string, like bla Bla 8.05/2020 \n BLAH bla15/05-2020 blaa. As one could observe, instead of / the date can have . or -, not necessary at the same time.

Some explaining

More specifically it can find dates of format day , moth year. Day is an one digit integer or a zero followed by one digit integer or 1 or 2 followed by an one digit integer or a 3 followed by 0 or 1. Month is an one digit integer or a zero followed by one digit integer or 1 followed by 0, 1, or 2. Year is the number 20 followed by any number between 00 and 99.

Useful notes

One can add more date splitting symbols by adding | symbol at the end of both (.|-|\/). For example for adding -- one would do (.|-|\/|--)

To have years outside of this millennium one has to modify (20[0-9][0-9]) to ([0-9][0-9][0-9][0-9])

Maven home (M2_HOME) not being picked up by IntelliJ IDEA

If M2_HOME is configured to point to the Maven home directory then:

  1. Go to File -> Settings
  2. Search for Maven
  3. Select Runner
  4. Insert in the field VM Options the following string:


Click Apply and OK

wp-admin shows blank page, how to fix it?

I was also facing same problem but i renamed contact-form-7 plugin from /wp-content/plugins directory to contact-form-7-rename and problem solved.

So this is due to unsupportable plugins or theme.

How to align a div to the top of its parent but keeping its inline-block behaviour?

Use vertical-align:top; for the element you want at the top, as I have demonstrated on your jsfiddle.

Using new line(\n) in string and rendering the same in HTML

Set your css in the table cell to


document.body.innerHTML = 'First line\nSecond line\nThird line';
body{ white-space:pre-wrap; }

How to delete multiple pandas (python) dataframes from memory to save RAM?

del statement does not delete an instance, it merely deletes a name.

When you do del i, you are deleting just the name i - but the instance is still bound to some other name, so it won't be Garbage-Collected.

If you want to release memory, your dataframes has to be Garbage-Collected, i.e. delete all references to them.

If you created your dateframes dynamically to list, then removing that list will trigger Garbage Collection.

>>> lst = [pd.DataFrame(), pd.DataFrame(), pd.DataFrame()]
>>> del lst     # memory is released

If you created some variables, you have to delete them all.

>>> a, b, c = pd.DataFrame(), pd.DataFrame(), pd.DataFrame()
>>> lst = [a, b, c]
>>> del a, b, c # dfs still in list
>>> del lst     # memory release now

Injecting content into specific sections from a partial view ASP.NET MVC 3 with Razor View Engine

I had this issue today. I'll add a workaround that uses <script defer> as I didn't see the other answers mention it.

//on a JS file somewhere (i.e partial-view-caller.js)
(() => <your partial view script>)();

//in your Partial View
<script src="~/partial-view-caller.js" defer></script>

//you can actually just straight call your partial view script living in an external file - I just prefer having an initialization method :)

Code above is an excerpt from a quick post I made about this question.

Assert a function/method was not called using Mock

You can check the called attribute, but if your assertion fails, the next thing you'll want to know is something about the unexpected call, so you may as well arrange for that information to be displayed from the start. Using unittest, you can check the contents of call_args_list instead:

self.assertItemsEqual(my_var.call_args_list, [])

When it fails, it gives a message like this:

AssertionError: Element counts were not equal:
First has 0, Second has 1:  call('first argument', 4)

SSH -L connection successful, but localhost port forwarding not working "channel 3: open failed: connect failed: Connection refused"

Posting this to help someone.


channel 2: open failed: connect failed: Connection refused
debug1: channel 2: free: direct-tcpip:
   listening port 8890 for port 8890,
   connect from ::1 port 52337 to ::1 port 8890, nchannels 8

My scenario; i had to use the remote server as a bastion host to connect elsewhere. Final Destination/Target:, port 8890. Through intermediary server with public ip:

SSH local port forwarding command:

ssh -i ~/keys/dev.tst -vnNT -L :8890:
[email protected]

What the problem was: There was no service bound on port 8890 in the target host. i had forgotten to start the service.

How did i trouble shoot:

SSH into bastion host and then do curl.

Hope this helps.

What's the difference between a 302 and a 307 redirect?

302 is temporary redirect, which is generated by the server whereas 307 is internal redirect response generated by the browser. Internal redirect means that redirect is done automatically by browser internally, basically the browser alters the entered url from http to https in get request by itself before making the request so request for unsecured connection is never made to the internet. Whether browser will alter the url to https or not depends upon the hsts preload list that comes preinstalled with the browser. You can also add any site which support https to the list by entering the domain in the hsts preload list of your own browser which is at chrome://net-internals/#hsts.One more thing website domains can be added by their owners to preload list by filling up the form at so that it comes preinstalled in browsers for every user even though I mention you can do particularly for yourself also.

Let me explain with an example:
I made a get request to which supports only https and I don't have that domain in my hsts preload list on my browser as site owner has not registered for it to come with preinstalled hsts preload list. request and response headers
GET request for unsecure version of the site is redirected to secure version(see http header named location for that in response in above image).
Now I add the site to my own browser preload list by adding its domain in Add hsts domain form at chrome://net-internals/#hsts, which modifies my personal preload list on my chrome browser.Be sure to select include subdomains for STS option there.
Let's see the request and response for the same website now after adding it to hsts preload list.
request and response headers
you can see the internal redirect 307 there in response headers, actually this response is generated by your browser not by server.
Also HSTS preload list can help prevent users reach the unsecure version of site as 302 redirect are prone to mitm attacks.
Hope I somewhat helped you understand more about redirects.

Maven Jacoco Configuration - Exclude classes/packages from report not working

you can configure the coverage exclusion in the sonar properties, outside of the configuration of the jacoco plugin:


and remember to remove the exclusion settings from the plugin

How to solve PHP error 'Notice: Array to string conversion in...'

$result = ob_get_clean();

if you want to capture the result in a variable

How do I get total physical memory size using PowerShell without WMI?

If you don't want to use WMI, I can suggest systeminfo.exe. But, there may be a better way to do that.

(systeminfo | Select-String 'Total Physical Memory:').ToString().Split(':')[1].Trim()

select count(*) from select

You're missing a FROM and you need to give the subquery an alias.

  SELECT DISTINCT a.my_id, a.last_name, a.first_name, b.temp_val
   FROM dbo.Table_A AS a 
   INNER JOIN dbo.Table_B AS b 
   ON a.a_id = b.a_id
) AS subquery;

org.apache.jasper.JasperException: Unable to compile class for JSP:

include your Member Class to your jsp :

<%@ page import="pageNumber.*, java.util.*,*,yourMemberPackage.Member" %>

How to remove td border with html?

<table border="1" cellspacing="0" cellpadding="0">
            <table border="0">

Comparing Dates in Oracle SQL

31-DEC-95 isn't a string, nor is 20-JUN-94. They're numbers with some extra stuff added on the end. This should be '31-DEC-95' or '20-JUN-94' - note the single quote, '. This will enable you to do a string comparison.

However, you're not doing a string comparison; you're doing a date comparison. You should transform your string into a date. Either by using the built-in TO_DATE() function, or a date literal.


select employee_id
  from employee
 where employee_date_hired > to_date('31-DEC-95','DD-MON-YY')

This method has a few unnecessary pitfalls

  • As a_horse_with_no_name noted in the comments, DEC, doesn't necessarily mean December. It depends on your NLS_DATE_LANGUAGE and NLS_DATE_FORMAT settings. To ensure that your comparison with work in any locale you can use the datetime format model MM instead
  • The year '95 is inexact. You know you mean 1995, but what if it was '50, is that 1950 or 2050? It's always best to be explicit
select employee_id
  from employee
 where employee_date_hired > to_date('31-12-1995','DD-MM-YYYY')

Date literals

A date literal is part of the ANSI standard, which means you don't have to use an Oracle specific function. When using a literal you must specify your date in the format YYYY-MM-DD and you cannot include a time element.

select employee_id
  from employee
 where employee_date_hired > date '1995-12-31'

Remember that the Oracle date datatype includes a time elemement, so the date without a time portion is equivalent to 1995-12-31 00:00:00.

If you want to include a time portion then you'd have to use a timestamp literal, which takes the format YYYY-MM-DD HH24:MI:SS[.FF0-9]

select employee_id
  from employee
 where employee_date_hired > timestamp '1995-12-31 12:31:02'

Further information

NLS_DATE_LANGUAGE is derived from NLS_LANGUAGE and NLS_DATE_FORMAT is derived from NLS_TERRITORY. These are set when you initially created the database but they can be altered by changing your inialization parameters file - only if really required - or at the session level by using the ALTER SESSION syntax. For instance:

alter session set nls_date_format = 'DD.MM.YYYY HH24:MI:SS';

This means:

  • DD numeric day of the month, 1 - 31
  • MM numeric month of the year, 01 - 12 ( January is 01 )
  • YYYY 4 digit year - in my opinion this is always better than a 2 digit year YY as there is no confusion with what century you're referring to.
  • HH24 hour of the day, 0 - 23
  • MI minute of the hour, 0 - 59
  • SS second of the minute, 0-59

You can find out your current language and date language settings by querying V$NLS_PARAMETERSs and the full gamut of valid values by querying V$NLS_VALID_VALUES.

Further reading

Incidentally, if you want the count(*) you need to group by employee_id

select employee_id, count(*)
  from employee
 where employee_date_hired > date '1995-12-31'
 group by employee_id

This gives you the count per employee_id.

What is the purpose of meshgrid in Python / NumPy?

Basic Idea

Given possible x values, xs, (think of them as the tick-marks on the x-axis of a plot) and possible y values, ys, meshgrid generates the corresponding set of (x, y) grid points---analogous to set((x, y) for x in xs for y in yx). For example, if xs=[1,2,3] and ys=[4,5,6], we'd get the set of coordinates {(1,4), (2,4), (3,4), (1,5), (2,5), (3,5), (1,6), (2,6), (3,6)}.

Form of the Return Value

However, the representation that meshgrid returns is different from the above expression in two ways:

First, meshgrid lays out the grid points in a 2d array: rows correspond to different y-values, columns correspond to different x-values---as in list(list((x, y) for x in xs) for y in ys), which would give the following array:

   [[(1,4), (2,4), (3,4)],
    [(1,5), (2,5), (3,5)],
    [(1,6), (2,6), (3,6)]]

Second, meshgrid returns the x and y coordinates separately (i.e. in two different numpy 2d arrays):

   xcoords, ycoords = (
       array([[1, 2, 3],
              [1, 2, 3],
              [1, 2, 3]]),
       array([[4, 4, 4],
              [5, 5, 5],
              [6, 6, 6]]))
   # same thing using np.meshgrid:
   xcoords, ycoords = np.meshgrid([1,2,3], [4,5,6])
   # same thing without meshgrid:
   xcoords = np.array([xs] * len(ys)
   ycoords = np.array([ys] * len(xs)).T

Note, np.meshgrid can also generate grids for higher dimensions. Given xs, ys, and zs, you'd get back xcoords, ycoords, zcoords as 3d arrays. meshgrid also supports reverse ordering of the dimensions as well as sparse representation of the result.


Why would we want this form of output?

Apply a function at every point on a grid: One motivation is that binary operators like (+, -, *, /, **) are overloaded for numpy arrays as elementwise operations. This means that if I have a function def f(x, y): return (x - y) ** 2 that works on two scalars, I can also apply it on two numpy arrays to get an array of elementwise results: e.g. f(xcoords, ycoords) or f(*np.meshgrid(xs, ys)) gives the following on the above example:

array([[ 9,  4,  1],
       [16,  9,  4],
       [25, 16,  9]])

Higher dimensional outer product: I'm not sure how efficient this is, but you can get high-dimensional outer products this way:[1,2,3], [1,2], [1,2,3,4]), axis=0).

Contour plots in matplotlib: I came across meshgrid when investigating drawing contour plots with matplotlib for plotting decision boundaries. For this, you generate a grid with meshgrid, evaluate the function at each grid point (e.g. as shown above), and then pass the xcoords, ycoords, and computed f-values (i.e. zcoords) into the contourf function.

How to check if a string is a valid JSON string in JavaScript without using Try/Catch

I used a really simple method to check a string how it's a valid JSON or not.

function testJSON(text){
    if (typeof text!=="string"){
        return false;
        return true;
    catch (error){
        return false;

Result with a valid JSON string:

var input='["foo","bar",{"foo":"bar"}]';
testJSON(input); // returns true;

Result with a simple string;

var input='This is not a JSON string.';
testJSON(input); // returns false;

Result with an object:

var input={};
testJSON(input); // returns false;

Result with null input:

var input=null;
testJSON(input); // returns false;

The last one returns false because the type of null variables is object.

This works everytime. :)

SLF4J: Class path contains multiple SLF4J bindings

I just ignored/removed that jar file.

enter image description here

Create nice column output in python

I found this answer super-helpful and elegant, originally from here:

matrix = [["A", "B"], ["C", "D"]]

print('\n'.join(['\t'.join([str(cell) for cell in row]) for row in matrix]))


A   B
C   D

Autowiring fails: Not an managed Type

I got an very helpful advice from Oliver Gierke:

The last exception you get actually indicates a problem with your JPA setup. "Not a managed bean" means not a type the JPA provider is aware of. If you're setting up a Spring based JPA application I'd recommend to configure the "packagesToScan" property on the LocalContainerEntityManagerFactory you have configured to the package that contains your JPA entities. Alternatively you can list all your entity classes in persistence.xml, but that's usually more cumbersome.

The former error you got (NoClassDefFound) indicates the class mentioned is not available on the projects classpath. So you might wanna check the inter module dependencies you have. As the two relevant classes seem to be located in the same module it might also just be an issue with an incomplete deployment to Tomcat (WTP is kind of bitchy sometimes). I'd definitely recommend to run a test for verification (as you already did). As this seems to lead you to a different exception, I guess it's really some Eclipse glitch


Initializing select with AngularJS and ng-repeat

As suggested you need to use ng-options and unfortunately I believe you need to reference the array element for a default (unless the array is an array of strings).

The JavaScript:

function AppCtrl($scope) {

    $scope.operators = [
        {value: 'eq', displayName: 'equals'},
        {value: 'neq', displayName: 'not equal'}

        operator: $scope.operators[0]


<body ng-app ng-controller="AppCtrl">
<div>Operator is: {{filterCondition.operator.value}}</div>
<select ng-model="filterCondition.operator" ng-options="operator.displayName for operator in operators">

PostgreSQL - SQL state: 42601 syntax error

Your function would work like this:

CREATE OR REPLACE FUNCTION prc_tst_bulk(sql text)
RETURNS TABLE (name text, rowcount integer) AS 

WITH v_tb_person AS (' || sql || $x$)
SELECT name, count(*)::int FROM v_tb_person WHERE nome LIKE '%a%' GROUP BY name
SELECT name, count(*)::int FROM v_tb_person WHERE gender = 1 GROUP BY name$x$;

$$ LANGUAGE plpgsql;


SELECT * FROM prc_tst_bulk($$SELECT a AS name, b AS nome, c AS gender FROM tbl$$)
  • You cannot mix plain and dynamic SQL the way you tried to do it. The whole statement is either all dynamic or all plain SQL. So I am building one dynamic statement to make this work. You may be interested in the chapter about executing dynamic commands in the manual.

  • The aggregate function count() returns bigint, but you had rowcount defined as integer, so you need an explicit cast ::int to make this work

  • I use dollar quoting to avoid quoting hell.

However, is this supposed to be a honeypot for SQL injection attacks or are you seriously going to use it? For your very private and secure use, it might be ok-ish - though I wouldn't even trust myself with a function like that. If there is any possible access for untrusted users, such a function is a loaded footgun. It's impossible to make this secure.

Craig (a sworn enemy of SQL injection!) might get a light stroke, when he sees what you forged from his piece of code in the answer to your preceding question. :)

The query itself seems rather odd, btw. But that's beside the point here.

Handling back button in Android Navigation Component

Here is solution that should do what you want, but i think it is a bad solution, because it is going against Android Navigation component idea(letting the android handle the navigation).

Override "onBackPressed" inside your activity

override fun onBackPressed() {
    when(NavHostFragment.findNavController(nav_host_fragment) {> {
            val dialog=AlertDialog.Builder(this).setMessage("Hello").setPositiveButton("Ok", DialogInterface.OnClickListener { dialogInterface, i ->
        else -> {

Merge, update, and pull Git branches without using checkouts

As Amber said, fast-forward merges are the only case in which you could conceivably do this. Any other merge conceivably needs to go through the whole three-way merge, applying patches, resolving conflicts deal - and that means there need to be files around.

I happen to have a script around I use for exactly this: doing fast-forward merges without touching the work tree (unless you're merging into HEAD). It's a little long, because it's at least a bit robust - it checks to make sure that the merge would be a fast-forward, then performs it without checking out the branch, but producing the same results as if you had - you see the diff --stat summary of changes, and the entry in the reflog is exactly like a fast forward merge, instead of the "reset" one you get if you use branch -f. If you name it git-merge-ff and drop it in your bin directory, you can call it as a git command: git merge-ff.


_usage() {
    echo "Usage: git merge-ff <branch> <committish-to-merge>" 1>&2
    exit 1

_merge_ff() {

    branch_orig_hash="$(git show-ref -s --verify refs/heads/$branch 2> /dev/null)"
    if [ $? -ne 0 ]; then
        echo "Error: unknown branch $branch" 1>&2

    commit_orig_hash="$(git rev-parse --verify $commit 2> /dev/null)"
    if [ $? -ne 0 ]; then
        echo "Error: unknown revision $commit" 1>&2

    if [ "$(git symbolic-ref HEAD)" = "refs/heads/$branch" ]; then
        git merge $quiet --ff-only "$commit"
        if [ "$(git merge-base $branch_orig_hash $commit_orig_hash)" != "$branch_orig_hash" ]; then
            echo "Error: merging $commit into $branch would not be a fast-forward" 1>&2
            exit 1
        echo "Updating ${branch_orig_hash:0:7}..${commit_orig_hash:0:7}"
        if git update-ref -m "merge $commit: Fast forward" "refs/heads/$branch" "$commit_orig_hash" "$branch_orig_hash"; then
            if [ -z $quiet ]; then
                echo "Fast forward"
                git diff --stat "$branch@{1}" "$branch"
            echo "Error: fast forward using update-ref failed" 1>&2

while getopts "q" opt; do
    case $opt in
        q ) quiet="-q";;
        * ) ;;
shift $((OPTIND-1))

case $# in
    2 ) _merge_ff "$1" "$2";;
    * ) _usage

P.S. If anyone sees any issues with that script, please comment! It was a write-and-forget job, but I'd be happy to improve it.

How to list physical disks?

The only sure shot way to do this is to call CreateFile() on all \\.\Physicaldiskx where x is from 0 to 15 (16 is maximum number of disks allowed). Check the returned handle value. If invalid check GetLastError() for ERROR_FILE_NOT_FOUND. If it returns anything else then the disk exists but you cannot access it for some reason.

Set transparent background using ImageMagick and commandline prompt


color=$( convert filename.png -format "%[pixel:p{0,0}]" info:- )
convert filename.png -alpha off -bordercolor $color -border 1 \
    \( +clone -fuzz 30% -fill none -floodfill +0+0 $color \
       -alpha extract -geometry 200% -blur 0x0.5 \
       -morphology erode square:1 -geometry 50% \) \
    -compose CopyOpacity -composite -shave 1 outputfilename.png


This is rather a bit longer than the simple answers previously given, but it gives much better results: (1) The quality is superior due to antialiased alpha, and (2) only the background is removed as opposed to a single color. ("Background" is defined as approximately the same color as the top left pixel, using a floodfill from the picture edges.)

Additionally, the alpha channel is also eroded by half a pixel to avoid halos. Of course, ImageMagick's morphological operations don't (yet?) work at the subpixel level, so you can see I am blowing up the alpha channel to 200% before eroding.

Comparison of results

Here is a comparison of the simple approach ("-fuzz 2% -transparent white") versus my solution, when run on the ImageMagick logo. I've flattened both transparent images onto a saddle brown background to make the differences apparent (click for originals).

The simple replacement of white as transparent doesn't always work Antialiased alphachannel and floodfill looks much better

Notice how the Wizard's beard has disappeared in the simple approach. Compare the edges of the Wizard to see how antialiased alpha helps the figure blend smoothly into the background.

Of course, I completely admit there are times when you may wish to use the simpler solution. (For example: It's a heck of a lot easier to remember and if you're converting to GIF, you're limited to 1-bit alpha anyhow.)

mktrans shell script

Since it's unlikely you'll want to type this command repeatedly, I recommend wrapping it in a script. You can download a BASH shell script from github which performs my suggested solution. It can be run on multiple files in a directory and includes helpful comments in case you want to tweak things.

bg_removal script

By the way, ImageMagick actually comes with a script called "bg_removal" which uses floodfill in a similar manner as my solution. However, the results are not great because it still uses 1-bit alpha. Also, the bg_removal script runs slower and is a little bit trickier to use (it requires you to specify two different fuzz values). Here's an example of the output from bg_removal.

The bg_removal script: has beard, but lacks antialiasing

jQuery UI Slider (setting programmatically)

If you need change slider values from several input, use it:


<input type="text" id="amount">
<input type="text" id="amount2">
<div id="slider-range"></div>


    $( "#slider-range" ).slider({
    range: true,
    min: 0,
    max: 217,
    values: [ 0, 217 ],
    slide: function( event, ui ) {
        $( "#amount" ).val( ui.values[ 0 ] );
        $( "#amount2" ).val( ui.values[ 1 ] );

$("#amount").change(function() {
$("#amount2").change(function() {

How to generate sample XML documents from their DTD or XSD?

XML-XIG: XML Instance Generator

This opensource would be helpful.

How to capitalize first letter of each word, like a 2-word city?

The JavaScript function:

String.prototype.capitalize = function(){
       return this.replace( /(^|\s)([a-z])/g , function(m,p1,p2){ return p1+p2.toUpperCase(); } );

To use this function:

capitalizedString = someString.toLowerCase().capitalize();

Also, this would work on multiple words string.

To make sure the converted City name is injected into the database, lowercased and first letter capitalized, then you would need to use JavaScript before you send it over to server side. CSS simply styles, but the actual data would remain pre-styled. Take a look at this jsfiddle example and compare the alert message vs the styled output.

DLL References in Visual C++

You mention adding the additional include directory (C/C++|General) and additional lib dependency (Linker|Input), but have you also added the additional library directory (Linker|General)?

Including a sample error message might also help people answer the question since it's not even clear if the error is during compilation or linking.

Laravel Eloquent limit and offset

Please try like this,

return Article::where('id',$article)->with(['products'=>function($products, $offset, $limit) {
    return $products->offset($offset*$limit)->limit($limit);

Ternary operators in JavaScript without an "else"

First of all, a ternary expression is not a replacement for an if/else construct - it's an equivalent to an if/else construct that returns a value. That is, an if/else clause is code, a ternary expression is an expression, meaning that it returns a value.

This means several things:

  • use ternary expressions only when you have a variable on the left side of the = that is to be assigned the return value
  • only use ternary expressions when the returned value is to be one of two values (or use nested expressions if that is fitting)
  • each part of the expression (after ? and after : ) should return a value without side effects (the expression x = true returns true as all expressions return the last value, but it also changes x without x having any effect on the returned value)

In short - the 'correct' use of a ternary expression is

var resultofexpression = conditionasboolean ? truepart: falsepart;

Instead of your example condition ? x=true : null ;, where you use a ternary expression to set the value of x, you can use this:

 condition && (x = true);

This is still an expression and might therefore not pass validation, so an even better approach would be

 void(condition && x = true);

The last one will pass validation.

But then again, if the expected value is a boolean, just use the result of the condition expression itself

var x = (condition); // var x = (foo == "bar");


In relation to your sample, this is probably more appropriate:

defaults.slideshowWidth = defaults.slideshowWidth || obj.find('img').width()+'px';

Class is inaccessible due to its protection level

The code you posted does not produce the error messages you quoted. You should provide a (small) example that actually exhibits the problem.

Unit Tests not discovered in Visual Studio 2017

For me, I needed to run this, which updated all the nunit adapter links for the unit test projects:

Install-Package Nunit3TestAdapter

Recover unsaved SQL query scripts

Go to SSMS >> Tools >> Options >> Environment >> AutoRecover

There are two different settings:

1) Save AutoRecover Information Every Minutes

This option will save the SQL Query file at certain interval. Set this option to minimum value possible to avoid loss. If you have set this value to 5, in the worst possible case, you can lose last 5 minutes of the work.

2) Keep AutoRecover Information for Days

This option will preserve the AutoRecovery information for specified days. Though, I suggest in case of accident open SQL Server Management Studio right away and recover your file. Do not procrastinate this important task for future dates.

PHP find difference between two datetimes

Sorry my previous answer was wrong. If you are trying to take total elapsed time between time and timeout in the format Y-m-d H:i:s format, take diff between timeout and time in using DateTime object and format it as '%y-%m-%d %H:%i:%s'.

Error: unable to verify the first certificate in nodejs

I faced this issue few days back and this is the approach I followed and it works for me.

For me this was happening when i was trying to fetch data using axios or fetch libraries as i am under a corporate firewall, so we had certain particular certificates which node js certificate store was not able to point to.

So for my loclahost i followed this approach. I created a folder in my project and kept the entire chain of certificates in the folder and in my scripts for dev-server(package.json) i added this alongwith server script so that node js can reference the path.

"dev-server":set NODE_EXTRA_CA_CERTS=certificates/certs-bundle.crt

For my servers(different environments),I created a new environment variable as below and added it.I was using Openshift,but i suppose the concept will be same for others as well.


I didn't generate any certificate in my case as the entire chain of certificates was already available for me.

How to install and run phpize

Go to the downloaded folder and there you find config.m4. Open the terminal and run phpsize.

How to delete/unset the properties of a javascript object?

To blank it:


To remove it:

delete myObject["myVar"]

as you can see in duplicate answers

How do I get a plist as a Dictionary in Swift?

It is best to use native dictionaries and arrays because they have been optimized for use with swift. That being said you can use NS... classes in swift and I think this situation warrants that. Here is how you would implement it:

var path = NSBundle.mainBundle().pathForResource("Config", ofType: "plist")
var dict = NSDictionary(contentsOfFile: path)

So far (in my opinion) this is the easiest and most efficient way to access a plist, but in the future I expect that apple will add more functionality (such as using plist) into native dictionaries.

Authentication issues with WWW-Authenticate: Negotiate

Putting this information here for future readers' benefit.

  • 401 (Unauthorized) response header -> Request authentication header

  • Here are several WWW-Authenticate response headers. (The full list is at IANA: HTTP Authentication Schemes.)

    • WWW-Authenticate: Basic-> Authorization: Basic + token - Use for basic authentication
    • WWW-Authenticate: NTLM-> Authorization: NTLM + token (2 challenges)
    • WWW-Authenticate: Negotiate -> Authorization: Negotiate + token - used for Kerberos authentication
      • By the way: IANA has this angry remark about Negotiate: This authentication scheme violates both HTTP semantics (being connection-oriented) and syntax (use of syntax incompatible with the WWW-Authenticate and Authorization header field syntax).

You can set the Authorization: Basic header only when you also have the WWW-Authenticate: Basic header on your 401 challenge.

But since you have WWW-Authenticate: Negotiate this should be the case for Kerberos based authentication.

How to correctly dismiss a DialogFragment?

Kotlin Version of Terel answer

(fragmentManager.findFragmentByTag(TAG) as? DialogFragment)?.dismiss()

How to properly stop the Thread in Java?

You should always end threads by checking a flag in the run() loop (if any).

Your thread should look like this:

public class IndexProcessor implements Runnable {

    private static final Logger LOGGER = LoggerFactory.getLogger(IndexProcessor.class);
    private volatile boolean execute;

    public void run() {
        this.execute = true;
        while (this.execute) {
            try {
                Thread.sleep((long) 15000);

            } catch (InterruptedException e) {
                LOGGER.error("Exception", e);
                this.execute = false;

    public void stopExecuting() {
        this.execute = false;

Then you can end the thread by calling thread.stopExecuting(). That way the thread is ended clean, but this takes up to 15 seconds (due to your sleep). You can still call thread.interrupt() if it's really urgent - but the prefered way should always be checking the flag.

To avoid waiting for 15 seconds, you can split up the sleep like this:

        try {
            for (int i = 0; (i < 150) && this.execute; i++) {
                Thread.sleep((long) 100);

        } catch (InterruptedException e) {

Learning to write a compiler

As an starting point, it will be good to create a recursive descent parser (RDP) (let's say you want to create your own flavour of BASIC and build a BASIC interpreter) to understand how to write a compiler. I found the best information in Herbert Schild's C Power Users, chapter 7. This chapter refers to another book of H. Schildt "C The complete Reference" where he explains how to create a calculator (a simple expression parser). I found both books on eBay very cheap. You can check the code for the book if you go to or check in I found the same code but for C# in his latest book

Getting the last element of a split string array

And if you don't want to construct an array ...

var str = "how,are you doing, today?";
var res = str.replace(/(.*)([, ])([^, ]*$)/,"$3");

The breakdown in english is:

/(anything)(any separator once)(anything that isn't a separator 0 or more times)/

The replace just says replace the entire string with the stuff after the last separator.

So you can see how this can be applied generally. Note the original string is not modified.

Is there a way to get the git root directory in one command?

The man page for git-config (under Alias) says:

If the alias expansion is prefixed with an exclamation point, it will be treated as a shell command. [...] Note that shell commands will be executed from the top-level directory of a repository, which may not necessarily be the current directory.

So, on UNIX you can do:

git config --global --add alias.root '!pwd'

Detect Safari using jQuery

unfortunately the above examples will also detect android's default browser as Safari, which it is not. I used navigator.userAgent.indexOf('Safari') != -1 && navigator.userAgent.indexOf('Chrome') == -1 && navigator.userAgent.indexOf('Android') == -1

How to remove multiple deleted files in Git repository

The built in clean function can also be helpful...

git clean -fd

How to convert an array of key-value tuples into an object

easiest way to do it where array is of your JSON data :

var obj = {};
obj[Data[0]] = Data[1]

C# Syntax - Example of a Lambda Expression - ForEach() over Generic List

public static void Each<T>(this IEnumerable<T> items, Action<T> action) {
foreach (var item in items) {
} }

... and call it thusly:

myList.Each(x => { x.Enabled = false; });

Force DOM redraw/refresh on Chrome/Mac

2020: Lighter and stronger

The previous solutions don't work anymore for me.

I guess browsers optimize the drawing process by detecting more and more "useless" changes.

This solution makes the browser draw a clone to replace the original element. It works and is probably more sustainable:

const element = document.querySelector('selector');
if (element ) {
  const clone = element.cloneNode(true);

tested on Chrome 80 / Edge 80 / Firefox 75

How to write a file with C in Linux?

You need to write() the read() data into the new file:

ssize_t nrd;
int fd;
int fd1;

fd = open(aa[1], O_RDONLY);
fd1 = open(aa[2], O_CREAT | O_WRONLY, S_IRUSR | S_IWUSR);
while (nrd = read(fd,buffer,50)) {


Update: added the proper opens...

Btw, the O_CREAT can be OR'd (O_CREAT | O_WRONLY). You are actually opening too many file handles. Just do the open once.

MySQL Workbench not displaying query results

I have updated macOS to 10.13.4 and it works.

Creating a select box with a search option

Full option searchable select box

This also supports Control buttons keyboards such as ArrowDown ArrowUp and Enter keys

function filterFunction(that, event) {_x000D_
    let container, input, filter, li, input_val;_x000D_
    container = $(that).closest(".searchable");_x000D_
    input_val = container.find("input").val().toUpperCase();_x000D_
    if (["ArrowDown", "ArrowUp", "Enter"].indexOf(event.key) != -1) {_x000D_
        keyControl(event, container)_x000D_
    } else {_x000D_
        li = container.find("ul li");_x000D_
        li.each(function (i, obj) {_x000D_
            if ($(this).text().toUpperCase().indexOf(input_val) > -1) {_x000D_
            } else {_x000D_
        container.find("ul li").removeClass("selected");_x000D_
        setTimeout(function () {_x000D_
            container.find("ul li:visible").first().addClass("selected");_x000D_
        }, 100)_x000D_
function keyControl(e, container) {_x000D_
    if (e.key == "ArrowDown") {_x000D_
        if (container.find("ul li").hasClass("selected")) {_x000D_
            if (container.find("ul li:visible").index(container.find("ul li.selected")) + 1 < container.find("ul li:visible").length) {_x000D_
                container.find("ul li.selected").removeClass("selected").nextAll().not('[style*="display: none"]').first().addClass("selected");_x000D_
        } else {_x000D_
            container.find("ul li:first-child").addClass("selected");_x000D_
    } else if (e.key == "ArrowUp") {_x000D_
        if (container.find("ul li:visible").index(container.find("ul li.selected")) > 0) {_x000D_
            container.find("ul li.selected").removeClass("selected").prevAll().not('[style*="display: none"]').first().addClass("selected");_x000D_
    } else if (e.key == "Enter") {_x000D_
        container.find("input").val(container.find("ul li.selected").text()).blur();_x000D_
        onSelect(container.find("ul li.selected").text())_x000D_
    container.find("ul li.selected")[0].scrollIntoView({_x000D_
        behavior: "smooth",_x000D_
function onSelect(val) {_x000D_
$(".searchable input").focus(function () {_x000D_
    $(this).closest(".searchable").find("ul li").show();_x000D_
$(".searchable input").blur(function () {_x000D_
    let that = this;_x000D_
    setTimeout(function () {_x000D_
    }, 300);_x000D_
$(document).on('click', '.searchable ul li', function () {_x000D_
$(".searchable ul li").hover(function () {_x000D_
    $(this).closest(".searchable").find("ul li.selected").removeClass("selected");_x000D_
div.searchable {_x000D_
    width: 300px;_x000D_
    float: left;_x000D_
    margin: 0 15px;_x000D_
.searchable input {_x000D_
    width: 100%;_x000D_
    height: 50px;_x000D_
    font-size: 18px;_x000D_
    padding: 10px;_x000D_
    -webkit-box-sizing: border-box; /* Safari/Chrome, other WebKit */_x000D_
    -moz-box-sizing: border-box; /* Firefox, other Gecko */_x000D_
    box-sizing: border-box; /* Opera/IE 8+ */_x000D_
    display: block;_x000D_
    font-weight: 400;_x000D_
    line-height: 1.6;_x000D_
    color: #495057;_x000D_
    background-color: #fff;_x000D_
    background-clip: padding-box;_x000D_
    border: 1px solid #ced4da;_x000D_
    border-radius: .25rem;_x000D_
    transition: border-color .15s ease-in-out, box-shadow .15s ease-in-out;_x000D_
    background: url("data:image/svg+xml;charset=utf-8,%3Csvg xmlns='' viewBox='0 0 4 5'%3E%3Cpath fill='%23343a40' d='M2 0L0 2h4zm0 5L0 3h4z'/%3E%3C/svg%3E") no-repeat right .75rem center/8px 10px;_x000D_
.searchable ul {_x000D_
    display: none;_x000D_
    list-style-type: none;_x000D_
    background-color: #fff;_x000D_
    border-radius: 0 0 5px 5px;_x000D_
    border: 1px solid #add8e6;_x000D_
    border-top: none;_x000D_
    max-height: 180px;_x000D_
    margin: 0;_x000D_
    overflow-y: scroll;_x000D_
    overflow-x: hidden;_x000D_
    padding: 0;_x000D_
.searchable ul li {_x000D_
    padding: 7px 9px;_x000D_
    border-bottom: 1px solid #e1e1e1;_x000D_
    cursor: pointer;_x000D_
    color: #6e6e6e;_x000D_
.searchable ul li.selected {_x000D_
    background-color: #e8e8e8;_x000D_
    color: #333;_x000D_
<script src=""></script>_x000D_
<div class="searchable">_x000D_
    <input type="text" placeholder="search countries" onkeyup="filterFunction(this,event)">_x000D_
        <li>Iran (Islamic Republic of)</li>_x000D_
        <li>Lao People's Democratic Republic</li>_x000D_
        <li>Micronesia (Federated States of)</li>_x000D_

SSRS chart does not show all labels on Horizontal axis

image: reporting services line chart horizontal axis properties

To see all dates on the report; Set Axis Type to Scalar, Set Interval to 1 -Jump Labels section Set disable auto-fit set label rotation angle as you desire.

These would help.

Set value of input instead of sendKeys() - Selenium WebDriver nodejs

Try to set the element's value using the executeScript method of JavascriptExecutor:

WebDriver driver = new FirefoxDriver();
JavascriptExecutor jse = (JavascriptExecutor)driver;
jse.executeScript("document.getElementById('elementID').setAttribute('value', 'new value for element')");

AngularJS Dropdown required validation

You need to add a name attribute to your dropdown list, then you need to add a required attribute, and then you can reference the error using myForm.[input name].$error.required:


        <form name="myForm" ng-controller="Ctrl" ng-submit="save(myForm)" novalidate>
        <input type="text" name="txtServiceName" ng-model="ServiceName" required>
<span ng-show="myForm.txtServiceName.$error.required">Enter Service Name</span>
          <select name="service_id" class="Sitedropdown" style="width: 220px;"          
                  ng-options="service.ServiceID as service.ServiceName for service in services"
            <option value="">Select Service</option> 
          <span ng-show="myForm.service_id.$error.required">Select service</span>



        function Ctrl($scope) {
          $ = [
            {ServiceID: 1, ServiceName: 'Service1'},
            {ServiceID: 2, ServiceName: 'Service2'},
            {ServiceID: 3, ServiceName: 'Service3'}

    $ = function(myForm) {
    console.log('Selected Value: '+ myForm.service_id.$modelValue);
    alert('Data Saved! without validate');

Here's a working plunker.

How to "comment-out" (add comment) in a batch/cmd?

Use :: or REM

::   commenttttttttttt
REM  commenttttttttttt

BUT (as people noted):

  • :: doesn't work inline; add & character:
    your commands here & :: commenttttttttttt
  • Inside nested parts (IF/ELSE, FOR loops, etc...) :: should be followed with normal line, otherwise it gives error (use REM there).
  • :: may also fail within setlocal ENABLEDELAYEDEXPANSION

How to declare and use 1D and 2D byte arrays in Verilog?

In addition to Marty's excellent Answer, the SystemVerilog specification offers the byte data type. The following declares a 4x8-bit variable (4 bytes), assigns each byte a value, then displays all values:

module tb;

byte b [4];

initial begin
    foreach (b[i]) b[i] = 1 << i;
    foreach (b[i]) $display("Address = %0d, Data = %b", i, b[i]);


This prints out:

Address = 0, Data = 00000001
Address = 1, Data = 00000010
Address = 2, Data = 00000100
Address = 3, Data = 00001000

This is similar in concept to Marty's reg [7:0] a [0:3];. However, byte is a 2-state data type (0 and 1), but reg is 4-state (01xz). Using byte also requires your tool chain (simulator, synthesizer, etc.) to support this SystemVerilog syntax. Note also the more compact foreach (b[i]) loop syntax.

The SystemVerilog specification supports a wide variety of multi-dimensional array types. The LRM can explain them better than I can; refer to IEEE Std 1800-2005, chapter 5.

How to compare DateTime without time via LINQ?

The Date property is not supported by LINQ to Entities -- you'll get an error if you try to use it on a DateTime field in a LINQ to Entities query. You can, however, trim dates using the DbFunctions.TruncateTime method.

var today = DateTime.Today;
var q = db.Games.Where(t => DbFunctions.TruncateTime(t.StartDate) >= today);

Automapper missing type map configuration or unsupported mapping - Error

I was trying to map an IEnumerable to an object. This is way I got this error. Maybe it helps.

Multiple Where clauses in Lambda expressions

Can be

x => x.Lists.Include(l => l.Title)
     .Where(l => l.Title != String.Empty && l.InternalName != String.Empty)


x => x.Lists.Include(l => l.Title)
     .Where(l => l.Title != String.Empty)
     .Where(l => l.InternalName != String.Empty)

When you are looking at Where implementation, you can see it accepts a Func(T, bool); that means:

  • T is your IEnumerable type
  • bool means it needs to return a boolean value

So, when you do

.Where(l => l.InternalName != String.Empty)
//     ^                   ^---------- boolean part
//     |------------------------------ "T" part

SFTP Libraries for .NET

We bought a Rebex File Transfer Pack, and all is fine. The API is easy, we haven't any problem with comunications, proxy servers etc...

But I havent chance to compare it with another SFTP/FTPS component.

Pass a PHP variable value through an HTML form

EDIT: After your comments, I understand that you want to pass variable through your form.

You can do this using hidden field:

<input type='hidden' name='var' value='<?php echo "$var";?>'/> 

In PHP action File:

   if(isset($_POST['var'])) $var=$_POST['var'];

Or using sessions: In your first page:


start_session(); should be placed at the beginning of your php page.

In PHP action File:

if(isset($_SESSION['var'])) $var=$_SESSION['var'];

First Answer:

You can also use $GLOBALS :

if (isset($_POST['save_exit']))

   echo $GLOBALS['var']; 


Check this documentation for more informations.

postgresql return 0 if returned value is null

(this answer was added to provide shorter and more generic examples to the question - without including all the case-specific details in the original question).

There are two distinct "problems" here, the first is if a table or subquery has no rows, the second is if there are NULL values in the query.

For all versions I've tested, postgres and mysql will ignore all NULL values when averaging, and it will return NULL if there is nothing to average over. This generally makes sense, as NULL is to be considered "unknown". If you want to override this you can use coalesce (as suggested by Luc M).

$ create table foo (bar int);

$ select avg(bar) from foo;

(1 row)

$ select coalesce(avg(bar), 0) from foo;
(1 row)

$ insert into foo values (3);
$ insert into foo values (9);
$ insert into foo values (NULL);
$ select coalesce(avg(bar), 0) from foo;
(1 row)

of course, "from foo" can be replaced by "from (... any complicated logic here ...) as foo"

Now, should the NULL row in the table be counted as 0? Then coalesce has to be used inside the avg call.

$ select coalesce(avg(coalesce(bar, 0)), 0) from foo;
(1 row)

How does delete[] know it's an array?

You cannot use delete for an array, and you cannot use delete [] for a non-array.

What is and how to fix System.TypeInitializationException error?

i. Please check the InnerException property of the TypeInitializationException

ii. Also, this may occur due to mismatch between the runtime versions of the assemblies. Please verify the runtime versions of the main assembly (calling application) and the referred assembly

InputStream from a URL


final InputStream is = new URL("").openStream();

/usr/lib/ version `GLIBCXX_3.4.15' not found

Same thing with gcc version 4.8.1 (GCC) and Had to copy it here /usr/lib/x86_64-linux-gnu on my ubuntu box.

Excel: VLOOKUP that returns true or false?

Just use a COUNTIF ! Much faster to write and calculate than the other suggestions.


Say you cell A1 should be 1 if the value of B1 is found in column C and otherwise it should be 2. How would you do that?

I would say if the value of B1 is found in column C, then A1 will be positive, otherwise it will be 0. Thats easily done with formula: =COUNTIF($C$1:$C$15,B1), which means: count the cells in range C1:C15 which are equal to B1.

You can combine COUNTIF with VLOOKUP and IF, and that's MUCH faster than using 2 lookups + ISNA. IF(COUNTIF(..)>0,LOOKUP(..),"Not found")

A bit of Googling will bring you tons of examples.

Disable automatic sorting on the first column when using jQuery DataTables

var table;

$(document).ready(function() {

    table = $('#userTable').DataTable({ 

        "processing": true, //Feature control the processing indicator.
        "serverSide": true, //Feature control DataTables' server-side processing mode.
        "order": [], //Initial no order.
         "aaSorting": [],
        // Load data for the table's content from an Ajax source
        "ajax": {
            "url": "<?php echo base_url().'admin/ajax_list';?>",
            "type": "POST"

        //Set column definition initialisation properties.
        "columnDefs": [
            "targets": [ ], //first column / numbering column
            "orderable": false, //set not orderable




"targets": [0]


 "targets": [ ]

What is float in Java?

The thing is that decimal numbers defaults to double. And since double doesn't fit into float you have to tell explicitely you intentionally define a float. So go with:

float b = 3.6f;

How to construct a std::string from a std::vector<char>?

I like Stefan’s answer (Sep 11 ’13) but would like to make it a bit stronger:

If the vector ends with a null terminator, you should not use (v.begin(), v.end()): you should use (or &v[0] for those prior to C++17).

If v does not have a null terminator, you should use (v.begin(), v.end()).

If you use begin() and end() and the vector does have a terminating zero, you’ll end up with a string "abc\0" for example, that is of length 4, but should really be only "abc".

Show/Hide Table Rows using Javascript classes

AngularJS directives ng-show, ng-hide allows to display and hide a row:

   <tr ng-show="rw.isExpanded">

A row will be visible when rw.isExpanded == true and hidden when rw.isExpanded == false. ng-hide performs the same task but requires inverse condition.

remove objects from array by object property

If you like short and self descriptive parameters or if you don't want to use splice and go with a straight forward filter or if you are simply a SQL person like me:

function removeFromArrayOfHash(p_array_of_hash, p_key, p_value_to_remove){
    return p_array_of_hash.filter((l_cur_row) => {return l_cur_row[p_key] != p_value_to_remove});

And a sample usage:

l_test_arr = 
         post_id: 1,
        post_content: "Hey I am the first hash with id 1"
        post_id: 2,
        post_content: "This is item 2"
        post_id: 1,
        post_content: "And I am the second hash with id 1"
        post_id: 3,
        post_content: "This is item 3"

 l_test_arr = removeFromArrayOfHash(l_test_arr, "post_id", 2); // gives both of the post_id 1 hashes and the post_id 3
 l_test_arr = removeFromArrayOfHash(l_test_arr, "post_id", 1); // gives only post_id 3 (since 1 was removed in previous line)

Find html label associated with a given input

All the other answers are extremely outdated!!

All you have to do is:


HTML5 has been supported by all of the major browsers for many years already. There is absolutely no reason that you should have to make this from scratch on your own or polyfill it! Literally just use input.labels and it solves all of your problems.

Is there an easy way to convert Android Application to IPad, IPhone

I'm not sure how helpful this answer is for your current application, but it may prove helpful for the next applications that you will be developing.

As iOS does not use Java like Android, your options are quite limited:

1) if your application is written mostly in C/C++ using JNI, you can write a wrapper and interface it with the iOS (i.e. provide callbacks from iOS to your JNI written function). There may be frameworks out there that help you do this easier, but there's still the problem of integrating the application and adapting it to the framework (and of course the fact that the application has to be written in C/C++).

2) rewrite it for iOS. I don't know whether there are any good companies that do this for you. Also, due to the variety of applications that can be written which can use different services and API, there may not be any software that can port it for you (I guess this kind of software is like a gold mine heh) or do a very good job at that.

3) I think that there are Java->C/C++ converters, but there won't help you at all when it comes to API differences. Also, you may find yourself struggling more to get the converted code working on any of the platforms rather than rewriting your application from scratch for iOS.

The problem depends quite a bit on the services and APIs your application is using. I haven't really look this up, but there may be some APIs that provide certain functionality in Android that iOS doesn't provide.

Using C/C++ and natively compiling it for the desired platform looks like the way to go for Android-iOS-Win7Mobile cross-platform development. This gets you somewhat of an application core/kernel which you can use to do the actual application logic.

As for the OS specific parts (APIs) that your application is using, you'll have to set up communication interfaces between them and your application's core.

SQL query for extracting year from a date

just pass the columnName as parameter of YEAR


another is to use DATE_FORMAT



I bet the value is varchar with the format MM/dd/YYYY, it that's the case,

SELECT YEAR(STR_TO_DATE('11/15/2012', '%m/%d/%Y'));

LAST RESORT if all the queries fail


SELECT SUBSTRING('11/15/2012', 7, 4)

How can I detect the touch event of an UIImageView?

First, you should place an UIButton and then either you can add a background image for this button, or you need to place an UIImageView over the button.


You can add the tap gesture to a UIImageView so that get the click action when tap on the UIImageView.

How to access pandas groupby dataframe by key

gb = df.groupby(['A'])

gb_groups = grouped_df.groups

If you are looking for selective groupby objects then, do: gb_groups.keys(), and input desired key into the following key_list..


key_list = [key1, key2, key3 and so on...]

for key, values in gb_groups.iteritems():
    if key in key_list:
        print df.ix[values], "\n"

Changing user agent on urllib2.urlopen

I answered a similar question a couple weeks ago.

There is example code in that question, but basically you can do something like this: (Note the capitalization of User-Agent as of RFC 2616, section 14.43.)

opener = urllib2.build_opener()
opener.addheaders = [('User-Agent', 'Mozilla/5.0')]
response ='')

How is a tag different from a branch in Git? Which should I use, here?

A tag is used to mark a version, more specifically it references a point in time on a branch. A branch is typically used to add features to a project.

Check key exist in python dict

Use the in keyword.

if 'apples' in d:
    if d['apples'] == 20:
        print('20 apples')
        print('Not 20 apples')

If you want to get the value only if the key exists (and avoid an exception trying to get it if it doesn't), then you can use the get function from a dictionary, passing an optional default value as the second argument (if you don't pass it it returns None instead):

if d.get('apples', 0) == 20:
    print('20 apples.')
    print('Not 20 apples.')

How to allow remote access to my WAMP server for Mobile(Android)

I assume you are using windows. Open the command prompt and type ipconfig and find out your local address (on your pc) it should look something like or where the end digit is the one that changes. It should be next to IPv4 Address.

If your WAMP does not use virtual hosts the next step is to enter that IP address on your phones browser ie If you have a virtual host then you will need root to edit the hosts file.

If you want to test the responsiveness / mobile design of your website you can change your user agent in chrome or other browsers to mimic a mobile.


Edit: Chrome dev tools now has a mobile debug tool where you can change the size of the viewport, spoof user agents, connections (4G, 3G etc).

If you get forbidden access then see this question WAMP error: Forbidden You don't have permission to access /phpmyadmin/ on this server. Basically, change the occurrances of deny,allow to allow,deny in the httpd.conf file. You can access this by the WAMP menu.

To eliminate possible causes of the issue for now set your config file to

<Directory />
    Options FollowSymLinks
    AllowOverride All
    Order allow,deny
    Allow from all
        Require all granted

As thatis working for my windows PC, if you have the directory config block as well change that also to allow all.

Config file that fixed the problem:

Problem was that the /www apache directory config block still had deny set as default and only allowed from localhost.

Pull request vs Merge request

As mentioned in previous answers, both serve almost same purpose. Personally I like git rebase and merge request (as in gitlab). It takes burden off of the reviewer/maintainer, making sure that while adding merge request, the feature branch includes all of the latest commits done on main branch after feature branch is created. Here is a very useful article explaining rebase in detail:

Error when creating a new text file with python?

If the file does not exists, open(name,'r+') will fail.

You can use open(name, 'w'), which creates the file if the file does not exist, but it will truncate the existing file.

Alternatively, you can use open(name, 'a'); this will create the file if the file does not exist, but will not truncate the existing file.

Run ssh and immediately execute command

ssh -t 'command; bash -l'

will execute the command and then start up a login shell when it completes. For example:

ssh -t [email protected] 'cd /some/path; bash -l'

Why is visible="false" not working for a plain html table?

For the best practice - use style="display:"

it will work every where..

Sorting 1 million 8-decimal-digit numbers with 1 MB of RAM

The trick is to represent the algorithms state, which is an integer multi-set, as a compressed stream of "increment counter"="+" and "output counter"="!" characters. For example, the set {0,3,3,4} would be represented as "!+++!!+!", followed by any number of "+" characters. To modify the multi-set you stream out the characters, keeping only a constant amount decompressed at a time, and make changes inplace before streaming them back in compressed form.


We know there are exactly 10^6 numbers in the final set, so there are at most 10^6 "!" characters. We also know that our range has size 10^8, meaning there are at most 10^8 "+" characters. The number of ways we can arrange 10^6 "!"s amongst 10^8 "+"s is (10^8 + 10^6) choose 10^6, and so specifying some particular arrangement takes ~0.965 MiB` of data. That'll be a tight fit.

We can treat each character as independent without exceeding our quota. There are exactly 100 times more "+" characters than "!" characters, which simplifies to 100:1 odds of each character being a "+" if we forget that they are dependent. Odds of 100:101 corresponds to ~0.08 bits per character, for an almost identical total of ~0.965 MiB (ignoring the dependency has a cost of only ~12 bits in this case!).

The simplest technique for storing independent characters with known prior probability is Huffman coding. Note that we need an impractically large tree (A huffman tree for blocks of 10 characters has an average cost per block of about 2.4 bits, for a total of ~2.9 Mib. A huffman tree for blocks of 20 characters has an average cost per block of about 3 bits, which is a total of ~1.8 MiB. We're probably going to need a block of size on the order of a hundred, implying more nodes in our tree than all the computer equipment that has ever existed can store.). However, ROM is technically "free" according to the problem and practical solutions that take advantage of the regularity in the tree will look essentially the same.


  • Have a sufficiently large huffman tree (or similar block-by-block compression data) stored in ROM
  • Start with a compressed string of 10^8 "+" characters.
  • To insert the number N, stream out the compressed string until N "+" characters have gone past then insert a "!". Stream the recompressed string back over the previous one as you go, keeping a constant amount of buffered blocks to avoid over/under-runs.
  • Repeat one million times: [input, stream decompress>insert>compress], then decompress to output

What's the best way to dedupe a table?

For deduplicate / dedupe / remove duplication / remove repeated rows / ??? ?? / ??? ?? ????, there are multiple ways.

  1. If duplicated rows are exact the same, use group by

    create table TABLE_NAME_DEDUP
    as select column1, column2, ... (all column names) from TABLE_NAME group by column1, column2, -- all column names

Then TABLE_NAME_DEDUP is the deduplicated table.

For example,

create table test (t1 varchar(5), t2 varchar(5));
insert into test  values ('12345', 'ssdlh');
insert into test  values ('12345', 'ssdlh');
create table test_dedup as
select * from test 
group by t1, t2;
--remove original table and rename dedup table to previous table
--this is not recommend in dev or qa. DROP table test; Alter table test_dedup rename to test;
  1. You have a rowid, the rowid has duplication but other columns are different Records partial same, this may happened in a transactional system while update a row, and the rows failed to update will have nulls. You want to remove the duplication

    create table test_dedup as select column1, column2, ... (all column names) from ( select * , row_number() over (partition by rowid order by column1, column2, ... (all column names except rowid) ) as cn from test ) where cn =1

This is using the feature that when you use order by, the null value will be ordered behind the non-null value.

create table test (rowid_ varchar(5), t1 varchar(5), t2 varchar(5));
insert into test  values ('12345', 'ssdlh', null);
insert into test  values ('12345', 'ssdlh', 'lhbzj');
create table test_dedup as
select rowid_, t1, t2 from
(select *
  , row_number() over (partition by rowid_ order by t1, t2) as cn
  from  test)
 where cn =1

--remove original table and rename dedup table to previous table
--this is not recommend in dev or qa. DROP table test; Alter table test_dedup rename to test;

JavaScript Form Submit - Confirm or Cancel Submission Dialog Box

Simple and easy :

<form onSubmit="return confirm('Do you want to submit?') ">_x000D_
  <input type="submit" />_x000D_

How can I make my string property nullable?

As others have pointed out, string is always nullable in C#. I suspect you are asking the question because you are not able to leave the middle name as null or blank? I suspect the problem is with your validation attributes, most likely the RegEx. I'm not able to fully parse RegEx in my head but I think your RegEx insists on the first character being present. I could be wrong - RegEx is hard. In any case, try commenting out your validation attributes and see if it works, then add them back in one at a time.

Get just the filename from a path in a Bash script

Some more alternative options because regexes (regi ?) are awesome!

Here is a Simple regex to do the job:


Example (grep):

 echo $FP | grep -oP "$regex"
 #Or using standard input
 grep -oP "$regex" <<< $FP

Example (awk):

 echo $FP | awk '{match($1, "$regex",a)}END{print a[0]}
 #Or using stardard input
 awk '{match($1, "$regex",a)}END{print a[0]} <<< $FP

If you need a more complicated regex: For example your path is wrapped in a string.

 StrFP="my string is awesome file: /hello/world/my/file/path/hello_my_filename.log sweet path bro."

 #this regex matches a string not containing / and ends with a period 
 #then at least one word character 
 #so its useful if you have an extension


 grep -oP "$regex" <<< $StrFP

 #alternatively you can get a little more complicated and use lookarounds
 #this regex matches a part of a string that starts with /  that does not contain a / 
 ##then uses the lazy operator ? to match any character at any amount (as little as possible hence the lazy)
 ##that is followed by a space
 ##this allows use to match just a file name in a string with a file path if it has an exntension or not
 ##also if the path doesnt have file it will match the last directory in the file path 
 ##however this will break if the file path has a space in it.


 #to fix the above problem you can use sed to remove spaces from the file path only
 ## as a side note unfortunately sed has limited regex capibility and it must be written out in long hand.
 NewStrFP=$(echo $StrFP | sed 's:\(/[a-z]*\)\( \)\([a-z]*/\):\1\3:g')
 grep -oP "$regex" <<< $NewStrFP

Total solution with Regexes:

This function can give you the filename with or without extension of a linux filepath even if the filename has multiple "."s in it. It can also handle spaces in the filepath and if the file path is embedded or wrapped in a string.

#you may notice that the sed replace has gotten really crazy looking
#I just added all of the allowed characters in a linux file path
function Get-FileName(){
    local FileString="$1"
    local NoExtension="$2"
    local FileString=$(echo $FileString | sed 's:\(/[a-zA-Z0-9\<\>\|\\\:\)\(\&\;\,\?\*]*\)\( \)\([a-zA-Z0-9\<\>\|\\\:\)\(\&\;\,\?\*]*/\):\1\3:g')

    local regex="(?<=/)[^/]*?(?=\s)"

    local FileName=$(echo $FileString | grep -oP "$regex")

    if [[ "$NoExtension" != "" ]]; then
        sed 's:\.[^\.]*$::g' <<< $FileName
        echo "$FileName"

## call the function with extension
Get-FileName "my string is awesome file: /hel lo/world/my/file test/path/hello_my_filename.log sweet path bro."

##call function without extension
Get-FileName "my string is awesome file: /hel lo/world/my/file test/path/hello_my_filename.log sweet path bro." "1"

If you have to mess with a windows path you can start with this one:


How to convert Milliseconds to "X mins, x seconds" in Java?

This answer is similar to some answers above. However, I feel that it would be beneficial because, unlike other answers, this will remove any extra commas or whitespace and handles abbreviation.

 * Converts milliseconds to "x days, x hours, x mins, x secs"
 * @param millis
 *            The milliseconds
 * @param longFormat
 *            {@code true} to use "seconds" and "minutes" instead of "secs" and "mins"
 * @return A string representing how long in days/hours/minutes/seconds millis is.
public static String millisToString(long millis, boolean longFormat) {
    if (millis < 1000) {
        return String.format("0 %s", longFormat ? "seconds" : "secs");
    String[] units = {
            "day", "hour", longFormat ? "minute" : "min", longFormat ? "second" : "sec"
    long[] times = new long[4];
    times[0] = TimeUnit.DAYS.convert(millis, TimeUnit.MILLISECONDS);
    millis -= TimeUnit.MILLISECONDS.convert(times[0], TimeUnit.DAYS);
    times[1] = TimeUnit.HOURS.convert(millis, TimeUnit.MILLISECONDS);
    millis -= TimeUnit.MILLISECONDS.convert(times[1], TimeUnit.HOURS);
    times[2] = TimeUnit.MINUTES.convert(millis, TimeUnit.MILLISECONDS);
    millis -= TimeUnit.MILLISECONDS.convert(times[2], TimeUnit.MINUTES);
    times[3] = TimeUnit.SECONDS.convert(millis, TimeUnit.MILLISECONDS);
    StringBuilder s = new StringBuilder();
    for (int i = 0; i < 4; i++) {
        if (times[i] > 0) {
            s.append(String.format("%d %s%s, ", times[i], units[i], times[i] == 1 ? "" : "s"));
    return s.toString().substring(0, s.length() - 2);

 * Converts milliseconds to "x days, x hours, x mins, x secs"
 * @param millis
 *            The milliseconds
 * @return A string representing how long in days/hours/mins/secs millis is.
public static String millisToString(long millis) {
    return millisToString(millis, false);

CodeIgniter -> Get current URL relative to base url

I see that this post is old. But in version CI v3 here is the answer:

echo $this->uri->uri_string();


How do I get into a Docker container's shell?

Another option is to use nsenter.

PID=$(docker inspect --format {{.State.Pid}} <container_name_or_ID>)
nsenter --target $PID --mount --uts --ipc --net --pid

Junit test case for database insert method with DAO and web service

public void testSearchManagementStaff() throws SQLException
    boolean res=true;
    ManagementDaoImp mdi=new ManagementDaoImp();
    boolean b=mdi.searchManagementStaff("[email protected]"," 123456");

How do I load an url in iframe with Jquery

here is Iframe in view:

<iframe class="img-responsive" id="ifmReport" width="1090" height="1200" >


Load it in script:

 $('#ifmReport').attr('src', '/ReportViewer/ReportViewer.aspx');

Should ol/ul be inside <p> or outside?

The second. The first is invalid.

  • A paragraph cannot contain a list.
  • A list cannot contain a paragraph unless that paragraph is contained entirely within a single list item.

A browser will handle it like so:

<!-- Start of paragraph -->
<!-- Start of ordered list. Paragraphs cannot contain lists. Insert </p> -->
<li>first element</li></ol>
<!-- A list item element. End of list -->
<!-- End of paragraph, but not inside paragraph, discard this tag to recover from the error -->
<p>other textetxet</p>
<!-- Another paragraph -->

SQL query for a carriage return in a string and ultimately removing carriage return

This also works


How can I merge the columns from two tables into one output?

Specifying the columns on your query should do the trick:

select a.col1, b.col2, a.col3, b.col4, a.category_id 
from items_a a, items_b b 
where a.category_id = b.category_id

should do the trick with regards to picking the columns you want.

To get around the fact that some data is only in items_a and some data is only in items_b, you would be able to do:

  coalesce(a.col1, b.col1) as col1, 
  coalesce(a.col2, b.col2) as col2,
  coalesce(a.col3, b.col3) as col3,
from items_a a, items_b b
where a.category_id = b.category_id

The coalesce function will return the first non-null value, so for each row if col1 is non null, it'll use that, otherwise it'll get the value from col2, etc.

NullPointerException: Attempt to invoke virtual method 'int java.util.ArrayList.size()' on a null object reference

You should initialize yours recordings. You are passing to adapter null

ArrayList<String> recordings = null; //You are passing this null

ASP.NET document.getElementById('<%=Control.ClientID%>'); returns null

Is Button1 visible? I mean, from the server side. Make sure Button1.Visible is true.

Controls that aren't Visible won't be rendered in HTML, so although they are assigned a ClientID, they don't actually exist on the client side.