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 should be considered to be "finished" once\nthe 'close' event is emitted.
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: ${input}`);\n});\nThe 'pause' event is emitted when one of the following occur:
input stream is paused.input stream is not paused and receives the SIGCONT event. (See\nevents SIGTSTP and SIGCONT)The listener function is called without passing any arguments.
\nFor example:
\nrl.on('pause', () =>{\n console.log('Readline paused.');\n});\nThe 'resume' event is emitted whenever the input stream is resumed.
The listener function is called without passing any arguments.
\nrl.on('resume', () =>{\n console.log('Readline resumed.');\n});\nThe 'SIGCONT' event is emitted when a Node.js process previously moved into\nthe background using <ctrl>-Z (i.e. SIGTSTP) is then brought back to the\nforeground using fg(1).
If the input stream was paused before the SIGSTP request, this event will\nnot be emitted.
The listener function is invoked without passing any arguments.
\nFor example:
\nrl.on('SIGCONT', () =>{\n // `prompt` will automatically resume the stream\n rl.prompt();\n});\nNote: The 'SIGCONT' event is not supported on Windows.
The 'SIGINT' event is emitted whenever the input stream receives a\n<ctrl>-C input, known typically as SIGINT. If there are no 'SIGINT' event\nlisteners registered when the input stream receives a SIGINT, the 'pause'\nevent will be emitted.
The listener function is invoked without passing any arguments.
\nFor example:
\nrl.on('SIGINT', () =>{\n rl.question('Are you sure you want to exit?', (answer) =>{\n if (answer.match(/^y(es)?$/i)) rl.pause();\n});\n});\nThe 'SIGTSPT' 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.\nCloses the Interface instance, relinquishing control on the input and\noutput streams. The 'close' event will also 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'});\nThe 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).
When called, the completer function is provided the current line entered by\nthe user, and is expected to return an Array with 2 entries:
For instance: [[substr1, substr2, ...], originalsubstring].
function completer(line){\n var completions = '.help .error .exit .quit .q'.split(' ');\n var hits = completions.filter((c) =>{return c.indexOf(line) == 0});\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 [Writable][]\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.
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\n[Readable][]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