Update how-to-prompt-for-command-line-input (#2051)

In accordance with issue #1977, I have updated the Article **how-to-prompt-for-command-line-input** with the following changes: 1. Exchanged **direct stdin usage** with **readline module** 2. Added example of `readline` module. 3. Some other miscellaneous updates and refactors.
nodejs · Feb 12, 2019 · dc47fa1 · dc47fa1
1 parent 8d435fb
commit dc47fa1
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diff --git a/locale/en/knowledge/command-line/how-to-prompt-for-command-line-input.md b/locale/en/knowledge/command-line/how-to-prompt-for-command-line-input.md
@@ -11,81 +11,96 @@ layout: knowledge-post.hbs
 
 So you've got a little CLI tool, but you want to be able to prompt a user for additional data after the script has started, rather than passing it in as a command line argument or putting it in a file.  To do this, you'll need to listen to STDIN ("standard input", i.e. your keyboard), which Node.js exposes for you as `process.stdin`, a readable stream.
 
-Streams are Node's way of dealing with evented I/O - they're a big topic, and you can read more about them (here).  For now, we're only going to deal with the Stream methods relevant to working with `process.stdin` so as to keep the examples easy.
-
-The first two Readable Stream methods you'll need to know about here are `pause()` and `resume()`.  Not every program needs to care whether or not you're pressing keys at a given moment, so `process.stdin` is paused by default. 
+Streams are Node's way of dealing with evented I/O - it's a big topic, and you can read more about them [here](https://nodejs.org/api/stream.html). For now, we're going to use node's `readline` module which is a wrapper around Standard I/O, suitable for taking user input from command line(terminal).
 
 Here's a simple example.  Try the following in a new file:
 
-      process.stdin.resume();
-      process.stdin.setEncoding('utf8');
-      var util = require('util');
-      
-      process.stdin.on('data', function (text) {
-        console.log('received data:', util.inspect(text));
-        if (text === 'quit\n') {
-          done();
-        }
-      });
-      
-      function done() {
-        console.log('Now that process.stdin is paused, there is nothing more to do.');
-        process.exit();
-      }
-      
-
-If all of this sounds complicated, or if you want a higher-level interface to this sort of thing, don't worry - as usual, the Node.js community has come to the rescue.  One particularly friendly module to use for this is Prompt, maintained by Nodejitsu.  It's available on `npm`:
-
-     npm install prompt
+```js
+const readline = require("readline");
+const rl = readline.createInterface({
+    input: process.stdin,
+    output: process.stdout
+});
+
+rl.question("What is your name ? ", function(name) {
+    rl.question("Which country do you belong ? ", function(country) {
+        console.log(`${name}, is a citizen of ${country}`);
+        rl.close();
+    });
+});
+
+rl.on("close", function() {
+    console.log("\nBYE BYE !!!");
+    process.exit(0);
+});
+```
+
+In the above code `readline.createInterface()` is used for creating an instance of `readline` by configuring the readable and the writable streams. The `input` key takes a readable stream like `process.stdin` or `fs.createReadStream('file.txt')` and the `output` key takes a writable stream like `process.stdout` or `process.stderr`.
+
+The `rl.question()` method displays the query by writing it to the `output`, waits for user input to be provided on `input`, then invokes the `callback` function passing the provided input as the first argument.
+
+NODE PRO TIP: Do remember to use `rl.close()` to close the transmitting otherwise the process will be left in the `idle` state.
+
+The last part of the code uses `rl.on()` method to add an event listener to the `close` event which simply `console.log` to the output stream and exits the process. This part is completely optional and can be removed at will. For more in-depth details and usage refer to the docs [here](https://nodejs.org/api/readline.html).
+
+If all of this sounds complicated, or if you want a higher-level interface to this sort of thing, don't worry - as usual, the Node.js community has come to the rescue.  One particularly friendly module to use for this is `prompt`, available on `npm`:
+
+```bash
+npm install prompt
+```
 
 Prompt is built to be easy - if your eyes started to glaze over as soon as you saw `Readable Stream`, then this is the section for you.  Compare the following to the example above:
 
-      var prompt = require('prompt');
-      
-      prompt.start();
-      
-      prompt.get(['username', 'email'], function (err, result) {
-        if (err) { return onErr(err); }
-        console.log('Command-line input received:');
-        console.log('  Username: ' + result.username);
-        console.log('  Email: ' + result.email);
-      });
-      
-      function onErr(err) {
-        console.log(err);
-        return 1;
-      }
-
-NODE PRO TIP: This short script also demonstrates proper error handling in node - errors are a callback's first argument, and `return` is used with the error handler so that the rest of the function doesn't execute when errors happen.  For more information, look (here).
+```js
+const prompt = require('prompt');
+
+prompt.start();
+
+prompt.get(['username', 'email'], function (err, result) {
+    if (err) { return onErr(err); }
+    console.log('Command-line input received:');
+    console.log('  Username: ' + result.username);
+    console.log('  Email: ' + result.email);
+});
+
+function onErr(err) {
+    console.log(err);
+    return 1;
+}
+```
+
+NODE PRO TIP: This short script also demonstrates proper error handling in node - errors are a callback's first argument, and `return` is used with the error handler so that the rest of the function doesn't execute when errors happen.
 
 Prompt also makes it trivial to handle a certain set of recurring properties that one might want to attach. 
 
-      var prompt = require('prompt');
-
-      var properties = [
-        {
-          name: 'username', 
-          validator: /^[a-zA-Z\s\-]+$/,
-          warning: 'Username must be only letters, spaces, or dashes'
-        },
-        {
-          name: 'password',
-          hidden: true
-        }
-      ];
-
-      prompt.start();
-
-      prompt.get(properties, function (err, result) {
-        if (err) { return onErr(err); }
-        console.log('Command-line input received:');
-        console.log('  Username: ' + result.username);
-        console.log('  Password: ' + result.password);
-      });
-
-      function onErr(err) {
-        console.log(err);
-        return 1;
-      }
-      
-For more information on Prompt, please see [the project's GitHub page](http://github.com/nodejitsu/node-prompt).
+```js
+const prompt = require('prompt');
+
+const properties = [
+    {
+        name: 'username', 
+        validator: /^[a-zA-Z\s\-]+$/,
+        warning: 'Username must be only letters, spaces, or dashes'
+    },
+    {
+        name: 'password',
+        hidden: true
+    }
+];
+
+prompt.start();
+
+prompt.get(properties, function (err, result) {
+    if (err) { return onErr(err); }
+    console.log('Command-line input received:');
+    console.log('  Username: ' + result.username);
+    console.log('  Password: ' + result.password);
+});
+
+function onErr(err) {
+    console.log(err);
+    return 1;
+}
+```
+
+For more information on Prompt, please see [the project's GitHub page](https://github.com/flatiron/prompt).