The readline module provides an interface for reading data from a Readable\nstream (such as process.stdin) one line at a time. It can be accessed using:
const readline = require('readline');\nThe following simple example illustrates the basic use of the readline module.
const readline = require('readline');\n\nconst rl = readline.createInterface({\n input: process.stdin,\n output: process.stdout\n});\n\nrl.question('What do you think of Node.js? ', (answer) => {\n // TODO: Log the answer in a database\n console.log(`Thank you for your valuable feedback: ${answer}`);\n\n rl.close();\n});\nNote Once this code is invoked, the Node.js application will not\nterminate until the readline.Interface is closed because the interface\nwaits for data to be received on the input stream.
Instances of the readline.Interface class are constructed using the\nreadline.createInterface() method. Every instance is associated with a\nsingle input Readable stream and a single output Writable stream.\nThe output stream is used to print prompts for user input that arrives on,\nand is read from, the input stream.
The 'close' event is emitted when one of the following occur:
rl.close() method is called and the readline.Interface instance has\nrelinquished control over the input and output streams;input stream receives its 'end' event;input stream receives <ctrl>-D to signal end-of-transmission (EOT);input stream receives <ctrl>-C to signal SIGINT and there is no\nSIGINT event listener registered on the readline.Interface instance.The listener function is called without passing any arguments.
\nThe readline.Interface instance is finished once the 'close' event is\nemitted.
The 'line' event is emitted whenever the input stream receives an\nend-of-line input (\\n, \\r, or \\r\\n). This usually occurs when the user\npresses the <Enter>, or <Return> keys.
The listener function is called with a string containing the single line of\nreceived input.
\nFor example:
\nrl.on('line', (input) => {\n console.log(`Received: ${input}`);\n});\nThe 'pause' event is emitted when one of the following occur:
input stream is paused.input stream is not paused and receives the SIGCONT event. (See\nevents SIGTSTP and SIGCONT)The listener function is called without passing any arguments.
\nFor example:
\nrl.on('pause', () => {\n console.log('Readline paused.');\n});\nThe 'resume' event is emitted whenever the input stream is resumed.
The listener function is called without passing any arguments.
\nrl.on('resume', () => {\n console.log('Readline resumed.');\n});\nThe 'SIGCONT' event is emitted when a Node.js process previously moved into\nthe background using <ctrl>-Z (i.e. SIGTSTP) is then brought back to the\nforeground using fg(1).
If the input stream was paused before the SIGTSTP request, this event will\nnot be emitted.
The listener function is invoked without passing any arguments.
\nFor example:
\nrl.on('SIGCONT', () => {\n // `prompt` will automatically resume the stream\n rl.prompt();\n});\nNote: The 'SIGCONT' event is not supported on Windows.
The 'SIGINT' event is emitted whenever the input stream receives a\n<ctrl>-C input, known typically as SIGINT. If there are no 'SIGINT' event\nlisteners registered when the input stream receives a SIGINT, the 'pause'\nevent will be emitted.
The listener function is invoked without passing any arguments.
\nFor example:
\nrl.on('SIGINT', () => {\n rl.question('Are you sure you want to exit? ', (answer) => {\n if (answer.match(/^y(es)?$/i)) rl.pause();\n });\n});\nThe 'SIGTSTP' event is emitted when the input stream receives a <ctrl>-Z\ninput, typically known as SIGTSTP. If there are no SIGTSTP event listeners\nregistered when the input stream receives a SIGTSTP, the Node.js process\nwill be sent to the background.
When the program is resumed using fg(1), the 'pause' and SIGCONT events\nwill be emitted. These can be used to resume the input stream.
The 'pause' and 'SIGCONT' events will not be emitted if the input was\npaused before the process was sent to the background.
The listener function is invoked without passing any arguments.
\nFor example:
\nrl.on('SIGTSTP', () => {\n // This will override SIGTSTP and prevent the program from going to the\n // background.\n console.log('Caught SIGTSTP.');\n});\nNote: The 'SIGTSTP' event is not supported on Windows.
The rl.close() method closes the readline.Interface instance and\nrelinquishes control over the input and output streams. When called,\nthe 'close' event will be emitted.
The rl.pause() method pauses the input stream, allowing it to be resumed\nlater if necessary.
Calling rl.pause() does not immediately pause other events (including\n'line') from being emitted by the readline.Interface instance.
The rl.prompt() method writes the readline.Interface instances configured\nprompt to a new line in output in order to provide a user with a new\nlocation at which to provide input.
When called, rl.prompt() will resume the input stream if it has been\npaused.
If the readline.Interface was created with output set to null or\nundefined the prompt is not written.
The rl.question() method displays the query by writing it to the output,\nwaits for user input to be provided on input, then invokes the callback\nfunction passing the provided input as the first argument.
When called, rl.question() will resume the input stream if it has been\npaused.
If the readline.Interface was created with output set to null or\nundefined the query is not written.
Example usage:
\nrl.question('What is your favorite food? ', (answer) => {\n console.log(`Oh, so your favorite food is ${answer}`);\n});\nNote: The callback function passed to rl.question() does not follow the\ntypical pattern of accepting an Error object or null as the first argument.\nThe callback is called with the provided answer as the only argument.
The rl.resume() method resumes the input stream if it has been paused.
The rl.setPrompt() method sets the prompt that will be written to output\nwhenever rl.prompt() is called.
The rl.write() method will write either data or a key sequence identified\nby key to the output. The key argument is supported only if output is\na TTY text terminal.
If key is specified, data is ignored.
When called, rl.write() will resume the input stream if it has been\npaused.
If the readline.Interface was created with output set to null or\nundefined the data and key are not written.
For example:
\nrl.write('Delete this!');\n// Simulate Ctrl+u to delete the line written previously\nrl.write(null, {ctrl: true, name: 'u'});\nNote: The rl.write() method will write the data to the readline\nInterface's input as if it were provided by the user.
The readline.clearLine() method clears current line of given TTY stream\nin a specified direction identified by dir.
The readline.clearScreenDown() method clears the given TTY stream from\nthe current position of the cursor down.
The readline.createInterface() method creates a new readline.Interface\ninstance.
For example:
\nconst readline = require('readline');\nconst rl = readline.createInterface({\n input: process.stdin,\n output: process.stdout\n});\nOnce the readline.Interface instance is created, the most common case is to\nlisten for the 'line' event:
rl.on('line', (line) => {\n console.log(`Received: ${line}`);\n});\nIf terminal is true for this instance then the output stream will get\nthe best compatibility if it defines an output.columns property and emits\na 'resize' event on the output if or when the columns ever change\n(process.stdout does this automatically when it is a TTY).
The completer function takes the current line entered by the user\nas an argument, and returns an Array with 2 entries:
For instance: [[substr1, substr2, ...], originalsubstring].
function completer(line) {\n const completions = '.help .error .exit .quit .q'.split(' ');\n const hits = completions.filter((c) => c.startsWith(line));\n // show all completions if none found\n return [hits.length ? hits : completions, line];\n}\nThe completer function can be called asynchronously if it accepts two\narguments:
function completer(linePartial, callback) {\n callback(null, [['123'], linePartial]);\n}\nThe readline.cursorTo() method moves cursor to the specified position in a\ngiven TTY stream.
The readline.emitKeypressEvents() method causes the given Readable\nstream to begin emitting 'keypress' events corresponding to received input.
Optionally, interface specifies a readline.Interface instance for which\nautocompletion is disabled when copy-pasted input is detected.
If the stream is a TTY, then it must be in raw mode.
Note: This is automatically called by any readline instance on its input\nif the input is a terminal. Closing the readline instance does not stop\nthe input from emitting 'keypress' events.
readline.emitKeypressEvents(process.stdin);\nif (process.stdin.isTTY)\n process.stdin.setRawMode(true);\nThe readline.moveCursor() method moves the cursor relative to its current\nposition in a given TTY stream.
The following example illustrates the use of readline.Interface class to\nimplement a small command-line interface:
const readline = require('readline');\nconst rl = readline.createInterface({\n input: process.stdin,\n output: process.stdout,\n prompt: 'OHAI> '\n});\n\nrl.prompt();\n\nrl.on('line', (line) => {\n switch (line.trim()) {\n case 'hello':\n console.log('world!');\n break;\n default:\n console.log(`Say what? I might have heard '${line.trim()}'`);\n break;\n }\n rl.prompt();\n}).on('close', () => {\n console.log('Have a great day!');\n process.exit(0);\n});\nA common use case for readline is to consume input from a filesystem\nReadable stream one line at a time, as illustrated in the following\nexample:
const readline = require('readline');\nconst fs = require('fs');\n\nconst rl = readline.createInterface({\n input: fs.createReadStream('sample.txt')\n});\n\nrl.on('line', (line) => {\n console.log(`Line from file: ${line}`);\n});\n