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<!doctype html> <html lang="en"> <head> <meta charset="utf-8"> <meta name="viewport" content="width=device-width"> <title>Readline | Node.js v10.19.0 Documentation</title> <link rel="stylesheet" href="assets/style.css"> <link rel="stylesheet" href="assets/sh.css"> <link rel="canonical" href="readline.html"> </head> <body class="alt apidoc" id="api-section-readline"> <div id="content" class="clearfix"> <div id="column2" class="interior"> <div id="intro" class="interior"> <a href="/" title="Go back to the home page"> Node.js </a> </div> <ul> <li><a class="nav-documentation" href="documentation.html">About these Docs</a></li> <li><a class="nav-synopsis" href="synopsis.html">Usage & Example</a></li> </ul> <div class="line"></div> <ul> <li><a class="nav-assert" href="assert.html">Assertion Testing</a></li> <li><a class="nav-async_hooks" href="async_hooks.html">Async Hooks</a></li> <li><a class="nav-buffer" href="buffer.html">Buffer</a></li> <li><a class="nav-addons" href="addons.html">C++ Addons</a></li> <li><a class="nav-n-api" href="n-api.html">C/C++ Addons - N-API</a></li> <li><a class="nav-child_process" href="child_process.html">Child Processes</a></li> <li><a class="nav-cluster" href="cluster.html">Cluster</a></li> <li><a class="nav-cli" href="cli.html">Command Line Options</a></li> <li><a class="nav-console" href="console.html">Console</a></li> <li><a class="nav-crypto" href="crypto.html">Crypto</a></li> <li><a class="nav-debugger" href="debugger.html">Debugger</a></li> <li><a class="nav-deprecations" href="deprecations.html">Deprecated APIs</a></li> <li><a class="nav-dns" href="dns.html">DNS</a></li> <li><a class="nav-domain" href="domain.html">Domain</a></li> <li><a class="nav-esm" href="esm.html">ECMAScript Modules</a></li> <li><a class="nav-errors" href="errors.html">Errors</a></li> <li><a class="nav-events" href="events.html">Events</a></li> <li><a class="nav-fs" href="fs.html">File System</a></li> <li><a class="nav-globals" href="globals.html">Globals</a></li> <li><a class="nav-http" href="http.html">HTTP</a></li> <li><a class="nav-http2" href="http2.html">HTTP/2</a></li> <li><a class="nav-https" href="https.html">HTTPS</a></li> <li><a class="nav-inspector" href="inspector.html">Inspector</a></li> <li><a class="nav-intl" href="intl.html">Internationalization</a></li> <li><a class="nav-modules" href="modules.html">Modules</a></li> <li><a class="nav-net" href="net.html">Net</a></li> <li><a class="nav-os" href="os.html">OS</a></li> <li><a class="nav-path" href="path.html">Path</a></li> <li><a class="nav-perf_hooks" href="perf_hooks.html">Performance Hooks</a></li> <li><a class="nav-process" href="process.html">Process</a></li> <li><a class="nav-punycode" href="punycode.html">Punycode</a></li> <li><a class="nav-querystring" href="querystring.html">Query Strings</a></li> <li><a class="nav-readline active" href="readline.html">Readline</a></li> <li><a class="nav-repl" href="repl.html">REPL</a></li> <li><a class="nav-stream" href="stream.html">Stream</a></li> <li><a class="nav-string_decoder" href="string_decoder.html">String Decoder</a></li> <li><a class="nav-timers" href="timers.html">Timers</a></li> <li><a class="nav-tls" href="tls.html">TLS/SSL</a></li> <li><a class="nav-tracing" href="tracing.html">Trace Events</a></li> <li><a class="nav-tty" href="tty.html">TTY</a></li> <li><a class="nav-dgram" href="dgram.html">UDP/Datagram</a></li> <li><a class="nav-url" href="url.html">URL</a></li> <li><a class="nav-util" href="util.html">Utilities</a></li> <li><a class="nav-v8" href="v8.html">V8</a></li> <li><a class="nav-vm" href="vm.html">VM</a></li> <li><a class="nav-worker_threads" href="worker_threads.html">Worker Threads</a></li> <li><a class="nav-zlib" href="zlib.html">Zlib</a></li> </ul> <div class="line"></div> <ul> <li><a class="nav-https-github-com-nodejs-node" href="https://github.com/nodejs/node">GitHub Repo & Issue Tracker</a></li> </ul> </div> <div id="column1" data-id="readline" class="interior"> <header> <h1>Node.js v10.19.0 Documentation</h1> <div id="gtoc"> <ul> <li> <a href="index.html" name="toc">Index</a> </li> <li> <a href="all.html">View on single page</a> </li> <li> <a href="readline.json">View as JSON</a> </li> <li class="version-picker"> <a href="#">View another version <span>▼</span></a> <ol class="version-picker"><li><a href="https://nodejs.org/docs/latest-v12.x/api/readline.html">12.x</a></li> <li><a href="https://nodejs.org/docs/latest-v11.x/api/readline.html">11.x</a></li> <li><a href="https://nodejs.org/docs/latest-v10.x/api/readline.html">10.x <b>LTS</b></a></li> <li><a href="https://nodejs.org/docs/latest-v9.x/api/readline.html">9.x</a></li> <li><a href="https://nodejs.org/docs/latest-v8.x/api/readline.html">8.x <b>LTS</b></a></li> <li><a href="https://nodejs.org/docs/latest-v7.x/api/readline.html">7.x</a></li> <li><a href="https://nodejs.org/docs/latest-v6.x/api/readline.html">6.x</a></li> <li><a href="https://nodejs.org/docs/latest-v5.x/api/readline.html">5.x</a></li> <li><a href="https://nodejs.org/docs/latest-v4.x/api/readline.html">4.x</a></li> <li><a href="https://nodejs.org/docs/latest-v0.12.x/api/readline.html">0.12.x</a></li> <li><a href="https://nodejs.org/docs/latest-v0.10.x/api/readline.html">0.10.x</a></li></ol> </li> <li class="edit_on_github"><a href="https://github.com/nodejs/node/edit/master/doc/api/readline.md"><span class="github_icon"><svg height="16" width="16" viewBox="0 0 16.1 16.1" fill="currentColor"><path d="M8 0a8 8 0 0 0-2.5 15.6c.4 0 .5-.2.5-.4v-1.5c-2 .4-2.5-.5-2.7-1 0-.1-.5-.9-.8-1-.3-.2-.7-.6 0-.6.6 0 1 .6 1.2.8.7 1.2 1.9 1 2.4.7 0-.5.2-.9.5-1-1.8-.3-3.7-1-3.7-4 0-.9.3-1.6.8-2.2 0-.2-.3-1 .1-2 0 0 .7-.3 2.2.7a7.4 7.4 0 0 1 4 0c1.5-1 2.2-.8 2.2-.8.5 1.1.2 2 .1 2.1.5.6.8 1.3.8 2.2 0 3-1.9 3.7-3.6 4 .3.2.5.7.5 1.4v2.2c0 .2.1.5.5.4A8 8 0 0 0 16 8a8 8 0 0 0-8-8z"/></svg></span>Edit on GitHub</a></li> </ul> </div> <hr> </header> <div id="toc"> <h2>Table of Contents</h2> <ul> <li><span class="stability_2"><a href="#readline_readline">Readline</a></span><ul> <li><a href="#readline_class_interface">Class: Interface</a><ul> <li><a href="#readline_event_close">Event: 'close'</a></li> <li><a href="#readline_event_line">Event: 'line'</a></li> <li><a href="#readline_event_pause">Event: 'pause'</a></li> <li><a href="#readline_event_resume">Event: 'resume'</a></li> <li><a href="#readline_event_sigcont">Event: 'SIGCONT'</a></li> <li><a href="#readline_event_sigint">Event: 'SIGINT'</a></li> <li><a href="#readline_event_sigtstp">Event: 'SIGTSTP'</a></li> <li><a href="#readline_rl_close">rl.close()</a></li> <li><a href="#readline_rl_pause">rl.pause()</a></li> <li><a href="#readline_rl_prompt_preservecursor">rl.prompt([preserveCursor])</a></li> <li><a href="#readline_rl_question_query_callback">rl.question(query, callback)</a></li> <li><a href="#readline_rl_resume">rl.resume()</a></li> <li><a href="#readline_rl_setprompt_prompt">rl.setPrompt(prompt)</a></li> <li><a href="#readline_rl_write_data_key">rl.write(data[, key])</a></li> <li><span class="stability_2"><a href="#readline_rl_symbol_asynciterator">rl[Symbol.asyncIterator]()</a></span></li> </ul> </li> <li><a href="#readline_readline_clearline_stream_dir">readline.clearLine(stream, dir)</a></li> <li><a href="#readline_readline_clearscreendown_stream">readline.clearScreenDown(stream)</a></li> <li><a href="#readline_readline_createinterface_options">readline.createInterface(options)</a><ul> <li><a href="#readline_use_of_the_completer_function">Use of the <code>completer</code> Function</a></li> </ul> </li> <li><a href="#readline_readline_cursorto_stream_x_y">readline.cursorTo(stream, x, y)</a></li> <li><a href="#readline_readline_emitkeypressevents_stream_interface">readline.emitKeypressEvents(stream[, interface])</a></li> <li><a href="#readline_readline_movecursor_stream_dx_dy">readline.moveCursor(stream, dx, dy)</a></li> <li><a href="#readline_example_tiny_cli">Example: Tiny CLI</a></li> <li><a href="#readline_example_read_file_stream_line_by_line">Example: Read File Stream Line-by-Line</a></li> </ul> </li> </ul> </div> <div id="apicontent"> <h1>Readline<span><a class="mark" href="#readline_readline" id="readline_readline">#</a></span></h1> <!--introduced_in=v0.10.0--> <div class="api_stability api_stability_2"><a href="documentation.html#documentation_stability_index">Stability: 2</a> - Stable</div><p>The <code>readline</code> module provides an interface for reading data from a <a href="stream.html#stream_readable_streams">Readable</a> stream (such as <a href="process.html#process_process_stdin"><code>process.stdin</code></a>) one line at a time. It can be accessed using:</p> <pre><code class="language-js">const readline = require('readline');</code></pre> <p>The following simple example illustrates the basic use of the <code>readline</code> module.</p> <pre><code class="language-js">const readline = require('readline'); const rl = readline.createInterface({ input: process.stdin, output: process.stdout }); rl.question('What do you think of Node.js? ', (answer) => { // TODO: Log the answer in a database console.log(`Thank you for your valuable feedback: ${answer}`); rl.close(); });</code></pre> <p>Once this code is invoked, the Node.js application will not terminate until the <code>readline.Interface</code> is closed because the interface waits for data to be received on the <code>input</code> stream.</p> <h2>Class: Interface<span><a class="mark" href="#readline_class_interface" id="readline_class_interface">#</a></span></h2> <div class="api_metadata"> <span>Added in: v0.1.104</span> </div><p>Instances of the <code>readline.Interface</code> class are constructed using the <code>readline.createInterface()</code> method. Every instance is associated with a single <code>input</code> <a href="stream.html#stream_readable_streams">Readable</a> stream and a single <code>output</code> <a href="stream.html#stream_writable_streams">Writable</a> stream. The <code>output</code> stream is used to print prompts for user input that arrives on, and is read from, the <code>input</code> stream.</p> <h3>Event: 'close'<span><a class="mark" href="#readline_event_close" id="readline_event_close">#</a></span></h3> <div class="api_metadata"> <span>Added in: v0.1.98</span> </div><p>The <code>'close'</code> event is emitted when one of the following occur:</p> <ul> <li>The <code>rl.close()</code> method is called and the <code>readline.Interface</code> instance has relinquished control over the <code>input</code> and <code>output</code> streams;</li> <li>The <code>input</code> stream receives its <code>'end'</code> event;</li> <li>The <code>input</code> stream receives <code><ctrl>-D</code> to signal end-of-transmission (EOT);</li> <li>The <code>input</code> stream receives <code><ctrl>-C</code> to signal <code>SIGINT</code> and there is no <code>'SIGINT'</code> event listener registered on the <code>readline.Interface</code> instance.</li> </ul> <p>The listener function is called without passing any arguments.</p> <p>The <code>readline.Interface</code> instance is finished once the <code>'close'</code> event is emitted.</p> <h3>Event: 'line'<span><a class="mark" href="#readline_event_line" id="readline_event_line">#</a></span></h3> <div class="api_metadata"> <span>Added in: v0.1.98</span> </div><p>The <code>'line'</code> event is emitted whenever the <code>input</code> stream receives an end-of-line input (<code>\n</code>, <code>\r</code>, or <code>\r\n</code>). This usually occurs when the user presses the <code><Enter></code>, or <code><Return></code> keys.</p> <p>The listener function is called with a string containing the single line of received input.</p> <pre><code class="language-js">rl.on('line', (input) => { console.log(`Received: ${input}`); });</code></pre> <h3>Event: 'pause'<span><a class="mark" href="#readline_event_pause" id="readline_event_pause">#</a></span></h3> <div class="api_metadata"> <span>Added in: v0.7.5</span> </div><p>The <code>'pause'</code> event is emitted when one of the following occur:</p> <ul> <li>The <code>input</code> stream is paused.</li> <li>The <code>input</code> stream is not paused and receives the <code>'SIGCONT'</code> event. (See events <a href="readline.html#readline_event_sigtstp"><code>'SIGTSTP'</code></a> and <a href="readline.html#readline_event_sigcont"><code>'SIGCONT'</code></a>.)</li> </ul> <p>The listener function is called without passing any arguments.</p> <pre><code class="language-js">rl.on('pause', () => { console.log('Readline paused.'); });</code></pre> <h3>Event: 'resume'<span><a class="mark" href="#readline_event_resume" id="readline_event_resume">#</a></span></h3> <div class="api_metadata"> <span>Added in: v0.7.5</span> </div><p>The <code>'resume'</code> event is emitted whenever the <code>input</code> stream is resumed.</p> <p>The listener function is called without passing any arguments.</p> <pre><code class="language-js">rl.on('resume', () => { console.log('Readline resumed.'); });</code></pre> <h3>Event: 'SIGCONT'<span><a class="mark" href="#readline_event_sigcont" id="readline_event_sigcont">#</a></span></h3> <div class="api_metadata"> <span>Added in: v0.7.5</span> </div><p>The <code>'SIGCONT'</code> event is emitted when a Node.js process previously moved into the background using <code><ctrl>-Z</code> (i.e. <code>SIGTSTP</code>) is then brought back to the foreground using <a href="http://man7.org/linux/man-pages/man1/fg.1p.html"><code>fg(1p)</code></a>.</p> <p>If the <code>input</code> stream was paused <em>before</em> the <code>SIGTSTP</code> request, this event will not be emitted.</p> <p>The listener function is invoked without passing any arguments.</p> <pre><code class="language-js">rl.on('SIGCONT', () => { // `prompt` will automatically resume the stream rl.prompt(); });</code></pre> <p>The <code>'SIGCONT'</code> event is <em>not</em> supported on Windows.</p> <h3>Event: 'SIGINT'<span><a class="mark" href="#readline_event_sigint" id="readline_event_sigint">#</a></span></h3> <div class="api_metadata"> <span>Added in: v0.3.0</span> </div><p>The <code>'SIGINT'</code> event is emitted whenever the <code>input</code> stream receives a <code><ctrl>-C</code> input, known typically as <code>SIGINT</code>. If there are no <code>'SIGINT'</code> event listeners registered when the <code>input</code> stream receives a <code>SIGINT</code>, the <code>'pause'</code> event will be emitted.</p> <p>The listener function is invoked without passing any arguments.</p> <pre><code class="language-js">rl.on('SIGINT', () => { rl.question('Are you sure you want to exit? ', (answer) => { if (answer.match(/^y(es)?$/i)) rl.pause(); }); });</code></pre> <h3>Event: 'SIGTSTP'<span><a class="mark" href="#readline_event_sigtstp" id="readline_event_sigtstp">#</a></span></h3> <div class="api_metadata"> <span>Added in: v0.7.5</span> </div><p>The <code>'SIGTSTP'</code> event is emitted when the <code>input</code> stream receives a <code><ctrl>-Z</code> input, typically known as <code>SIGTSTP</code>. If there are no <code>'SIGTSTP'</code> event listeners registered when the <code>input</code> stream receives a <code>SIGTSTP</code>, the Node.js process will be sent to the background.</p> <p>When the program is resumed using <a href="http://man7.org/linux/man-pages/man1/fg.1p.html"><code>fg(1p)</code></a>, the <code>'pause'</code> and <code>'SIGCONT'</code> events will be emitted. These can be used to resume the <code>input</code> stream.</p> <p>The <code>'pause'</code> and <code>'SIGCONT'</code> events will not be emitted if the <code>input</code> was paused before the process was sent to the background.</p> <p>The listener function is invoked without passing any arguments.</p> <pre><code class="language-js">rl.on('SIGTSTP', () => { // This will override SIGTSTP and prevent the program from going to the // background. console.log('Caught SIGTSTP.'); });</code></pre> <p>The <code>'SIGTSTP'</code> event is <em>not</em> supported on Windows.</p> <h3>rl.close()<span><a class="mark" href="#readline_rl_close" id="readline_rl_close">#</a></span></h3> <div class="api_metadata"> <span>Added in: v0.1.98</span> </div><p>The <code>rl.close()</code> method closes the <code>readline.Interface</code> instance and relinquishes control over the <code>input</code> and <code>output</code> streams. When called, the <code>'close'</code> event will be emitted.</p> <p>Calling <code>rl.close()</code> does not immediately stop other events (including <code>'line'</code>) from being emitted by the <code>readline.Interface</code> instance.</p> <h3>rl.pause()<span><a class="mark" href="#readline_rl_pause" id="readline_rl_pause">#</a></span></h3> <div class="api_metadata"> <span>Added in: v0.3.4</span> </div><p>The <code>rl.pause()</code> method pauses the <code>input</code> stream, allowing it to be resumed later if necessary.</p> <p>Calling <code>rl.pause()</code> does not immediately pause other events (including <code>'line'</code>) from being emitted by the <code>readline.Interface</code> instance.</p> <h3>rl.prompt([preserveCursor])<span><a class="mark" href="#readline_rl_prompt_preservecursor" id="readline_rl_prompt_preservecursor">#</a></span></h3> <div class="api_metadata"> <span>Added in: v0.1.98</span> </div><ul> <li><code>preserveCursor</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> If <code>true</code>, prevents the cursor placement from being reset to <code>0</code>.</li> </ul> <p>The <code>rl.prompt()</code> method writes the <code>readline.Interface</code> instances configured <code>prompt</code> to a new line in <code>output</code> in order to provide a user with a new location at which to provide input.</p> <p>When called, <code>rl.prompt()</code> will resume the <code>input</code> stream if it has been paused.</p> <p>If the <code>readline.Interface</code> was created with <code>output</code> set to <code>null</code> or <code>undefined</code> the prompt is not written.</p> <h3>rl.question(query, callback)<span><a class="mark" href="#readline_rl_question_query_callback" id="readline_rl_question_query_callback">#</a></span></h3> <div class="api_metadata"> <span>Added in: v0.3.3</span> </div><ul> <li><code>query</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> A statement or query to write to <code>output</code>, prepended to the prompt.</li> <li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> A callback function that is invoked with the user's input in response to the <code>query</code>.</li> </ul> <p>The <code>rl.question()</code> method displays the <code>query</code> by writing it to the <code>output</code>, waits for user input to be provided on <code>input</code>, then invokes the <code>callback</code> function passing the provided input as the first argument.</p> <p>When called, <code>rl.question()</code> will resume the <code>input</code> stream if it has been paused.</p> <p>If the <code>readline.Interface</code> was created with <code>output</code> set to <code>null</code> or <code>undefined</code> the <code>query</code> is not written.</p> <p>Example usage:</p> <pre><code class="language-js">rl.question('What is your favorite food? ', (answer) => { console.log(`Oh, so your favorite food is ${answer}`); });</code></pre> <p>The <code>callback</code> function passed to <code>rl.question()</code> does not follow the typical pattern of accepting an <code>Error</code> object or <code>null</code> as the first argument. The <code>callback</code> is called with the provided answer as the only argument.</p> <h3>rl.resume()<span><a class="mark" href="#readline_rl_resume" id="readline_rl_resume">#</a></span></h3> <div class="api_metadata"> <span>Added in: v0.3.4</span> </div><p>The <code>rl.resume()</code> method resumes the <code>input</code> stream if it has been paused.</p> <h3>rl.setPrompt(prompt)<span><a class="mark" href="#readline_rl_setprompt_prompt" id="readline_rl_setprompt_prompt">#</a></span></h3> <div class="api_metadata"> <span>Added in: v0.1.98</span> </div><ul> <li><code>prompt</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> </ul> <p>The <code>rl.setPrompt()</code> method sets the prompt that will be written to <code>output</code> whenever <code>rl.prompt()</code> is called.</p> <h3>rl.write(data[, key])<span><a class="mark" href="#readline_rl_write_data_key" id="readline_rl_write_data_key">#</a></span></h3> <div class="api_metadata"> <span>Added in: v0.1.98</span> </div><ul> <li><code>data</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> <li><code>key</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a><ul> <li><code>ctrl</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> <code>true</code> to indicate the <code><ctrl></code> key.</li> <li><code>meta</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> <code>true</code> to indicate the <code><Meta></code> key.</li> <li><code>shift</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> <code>true</code> to indicate the <code><Shift></code> key.</li> <li><code>name</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> The name of the a key.</li> </ul> </li> </ul> <p>The <code>rl.write()</code> method will write either <code>data</code> or a key sequence identified by <code>key</code> to the <code>output</code>. The <code>key</code> argument is supported only if <code>output</code> is a <a href="tty.html">TTY</a> text terminal.</p> <p>If <code>key</code> is specified, <code>data</code> is ignored.</p> <p>When called, <code>rl.write()</code> will resume the <code>input</code> stream if it has been paused.</p> <p>If the <code>readline.Interface</code> was created with <code>output</code> set to <code>null</code> or <code>undefined</code> the <code>data</code> and <code>key</code> are not written.</p> <pre><code class="language-js">rl.write('Delete this!'); // Simulate Ctrl+u to delete the line written previously rl.write(null, { ctrl: true, name: 'u' });</code></pre> <p>The <code>rl.write()</code> method will write the data to the <code>readline</code> <code>Interface</code>'s <code>input</code> <em>as if it were provided by the user</em>.</p> <h3>rl[Symbol.asyncIterator]()<span><a class="mark" href="#readline_rl_symbol_asynciterator" id="readline_rl_symbol_asynciterator">#</a></span></h3> <div class="api_metadata"> <details class="changelog"><summary>History</summary> <table> <tr><th>Version</th><th>Changes</th></tr> <tr><td>v11.4.0</td> <td><p><span>Added in: v11.4.0</span></p> </td></tr> <tr><td>v10.17.0</td> <td><p>Symbol.asyncIterator support is no longer experimental.</p> </td></tr> </table> </details> </div><div class="api_stability api_stability_2"><a href="documentation.html#documentation_stability_index">Stability: 2</a> - Stable</div><ul> <li>Returns: <a href="https://tc39.github.io/ecma262/#sec-asynciterator-interface" class="type"><AsyncIterator></a></li> </ul> <p>Create an <code>AsyncIterator</code> object that iterates through each line in the input stream as a string. This method allows asynchronous iteration of <code>readline.Interface</code> objects through <code>for</code>-<code>await</code>-<code>of</code> loops.</p> <p>Errors in the input stream are not forwarded.</p> <p>If the loop is terminated with <code>break</code>, <code>throw</code>, or <code>return</code>, <a href="#readline_rl_close"><code>rl.close()</code></a> will be called. In other words, iterating over a <code>readline.Interface</code> will always consume the input stream fully.</p> <p>A caveat with using this experimental API is that the performance is currently not on par with the traditional <code>'line'</code> event API, and thus it is not recommended for performance-sensitive applications. We expect this situation to improve in the future.</p> <pre><code class="language-js">async function processLineByLine() { const rl = readline.createInterface({ // ... }); for await (const line of rl) { // Each line in the readline input will be successively available here as // `line`. } }</code></pre> <h2>readline.clearLine(stream, dir)<span><a class="mark" href="#readline_readline_clearline_stream_dir" id="readline_readline_clearline_stream_dir">#</a></span></h2> <div class="api_metadata"> <span>Added in: v0.7.7</span> </div><ul> <li><code>stream</code> <a href="stream.html#stream_class_stream_writable" class="type"><stream.Writable></a></li> <li><code>dir</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a><ul> <li><code>-1</code> - to the left from cursor</li> <li><code>1</code> - to the right from cursor</li> <li><code>0</code> - the entire line</li> </ul> </li> </ul> <p>The <code>readline.clearLine()</code> method clears current line of given <a href="tty.html">TTY</a> stream in a specified direction identified by <code>dir</code>.</p> <h2>readline.clearScreenDown(stream)<span><a class="mark" href="#readline_readline_clearscreendown_stream" id="readline_readline_clearscreendown_stream">#</a></span></h2> <div class="api_metadata"> <span>Added in: v0.7.7</span> </div><ul> <li><code>stream</code> <a href="stream.html#stream_class_stream_writable" class="type"><stream.Writable></a></li> </ul> <p>The <code>readline.clearScreenDown()</code> method clears the given <a href="tty.html">TTY</a> stream from the current position of the cursor down.</p> <h2>readline.createInterface(options)<span><a class="mark" href="#readline_readline_createinterface_options" id="readline_readline_createinterface_options">#</a></span></h2> <div class="api_metadata"> <details class="changelog"><summary>History</summary> <table> <tr><th>Version</th><th>Changes</th></tr> <tr><td>v8.3.0, 6.11.4</td> <td><p>Remove max limit of <code>crlfDelay</code> option.</p> </td></tr> <tr><td>v6.6.0</td> <td><p>The <code>crlfDelay</code> option is supported now.</p> </td></tr> <tr><td>v6.3.0</td> <td><p>The <code>prompt</code> option is supported now.</p> </td></tr> <tr><td>v6.0.0</td> <td><p>The <code>historySize</code> option can be <code>0</code> now.</p> </td></tr> <tr><td>v0.1.98</td> <td><p><span>Added in: v0.1.98</span></p> </td></tr> </table> </details> </div><ul> <li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a><ul> <li><code>input</code> <a href="stream.html#stream_class_stream_readable" class="type"><stream.Readable></a> The <a href="stream.html#stream_readable_streams">Readable</a> stream to listen to. This option is <em>required</em>.</li> <li><code>output</code> <a href="stream.html#stream_class_stream_writable" class="type"><stream.Writable></a> The <a href="stream.html#stream_writable_streams">Writable</a> stream to write readline data to.</li> <li><code>completer</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> An optional function used for Tab autocompletion.</li> <li><code>terminal</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> <code>true</code> if the <code>input</code> and <code>output</code> streams should be treated like a TTY, and have ANSI/VT100 escape codes written to it. <strong>Default:</strong> checking <code>isTTY</code> on the <code>output</code> stream upon instantiation.</li> <li><code>historySize</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> Maximum number of history lines retained. To disable the history set this value to <code>0</code>. This option makes sense only if <code>terminal</code> is set to <code>true</code> by the user or by an internal <code>output</code> check, otherwise the history caching mechanism is not initialized at all. <strong>Default:</strong> <code>30</code>.</li> <li><code>prompt</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> The prompt string to use. <strong>Default:</strong> <code>'> '</code>.</li> <li><code>crlfDelay</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> If the delay between <code>\r</code> and <code>\n</code> exceeds <code>crlfDelay</code> milliseconds, both <code>\r</code> and <code>\n</code> will be treated as separate end-of-line input. <code>crlfDelay</code> will be coerced to a number no less than <code>100</code>. It can be set to <code>Infinity</code>, in which case <code>\r</code> followed by <code>\n</code> will always be considered a single newline (which may be reasonable for <a href="#readline_example_read_file_stream_line_by_line">reading files</a> with <code>\r\n</code> line delimiter). <strong>Default:</strong> <code>100</code>.</li> <li><code>removeHistoryDuplicates</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> If <code>true</code>, when a new input line added to the history list duplicates an older one, this removes the older line from the list. <strong>Default:</strong> <code>false</code>.</li> <li><code>escapeCodeTimeout</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The duration <code>readline</code> will wait for a character (when reading an ambiguous key sequence in milliseconds one that can both form a complete key sequence using the input read so far and can take additional input to complete a longer key sequence). <strong>Default:</strong> <code>500</code>.</li> </ul> </li> </ul> <p>The <code>readline.createInterface()</code> method creates a new <code>readline.Interface</code> instance.</p> <pre><code class="language-js">const readline = require('readline'); const rl = readline.createInterface({ input: process.stdin, output: process.stdout });</code></pre> <p>Once the <code>readline.Interface</code> instance is created, the most common case is to listen for the <code>'line'</code> event:</p> <pre><code class="language-js">rl.on('line', (line) => { console.log(`Received: ${line}`); });</code></pre> <p>If <code>terminal</code> is <code>true</code> for this instance then the <code>output</code> stream will get the best compatibility if it defines an <code>output.columns</code> property and emits a <code>'resize'</code> event on the <code>output</code> if or when the columns ever change (<a href="process.html#process_process_stdout"><code>process.stdout</code></a> does this automatically when it is a TTY).</p> <h3>Use of the <code>completer</code> Function<span><a class="mark" href="#readline_use_of_the_completer_function" id="readline_use_of_the_completer_function">#</a></span></h3> <p>The <code>completer</code> function takes the current line entered by the user as an argument, and returns an <code>Array</code> with 2 entries:</p> <ul> <li>An <code>Array</code> with matching entries for the completion.</li> <li>The substring that was used for the matching.</li> </ul> <p>For instance: <code>[[substr1, substr2, ...], originalsubstring]</code>.</p> <pre><code class="language-js">function completer(line) { const completions = '.help .error .exit .quit .q'.split(' '); const hits = completions.filter((c) => c.startsWith(line)); // show all completions if none found return [hits.length ? hits : completions, line]; }</code></pre> <p>The <code>completer</code> function can be called asynchronously if it accepts two arguments:</p> <pre><code class="language-js">function completer(linePartial, callback) { callback(null, [['123'], linePartial]); }</code></pre> <h2>readline.cursorTo(stream, x, y)<span><a class="mark" href="#readline_readline_cursorto_stream_x_y" id="readline_readline_cursorto_stream_x_y">#</a></span></h2> <div class="api_metadata"> <span>Added in: v0.7.7</span> </div><ul> <li><code>stream</code> <a href="stream.html#stream_class_stream_writable" class="type"><stream.Writable></a></li> <li><code>x</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> <li><code>y</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>The <code>readline.cursorTo()</code> method moves cursor to the specified position in a given <a href="tty.html">TTY</a> <code>stream</code>.</p> <h2>readline.emitKeypressEvents(stream[, interface])<span><a class="mark" href="#readline_readline_emitkeypressevents_stream_interface" id="readline_readline_emitkeypressevents_stream_interface">#</a></span></h2> <div class="api_metadata"> <span>Added in: v0.7.7</span> </div><ul> <li><code>stream</code> <a href="stream.html#stream_class_stream_readable" class="type"><stream.Readable></a></li> <li><code>interface</code> <a href="readline.html#readline_class_interface" class="type"><readline.Interface></a></li> </ul> <p>The <code>readline.emitKeypressEvents()</code> method causes the given <a href="stream.html#stream_readable_streams">Readable</a> stream to begin emitting <code>'keypress'</code> events corresponding to received input.</p> <p>Optionally, <code>interface</code> specifies a <code>readline.Interface</code> instance for which autocompletion is disabled when copy-pasted input is detected.</p> <p>If the <code>stream</code> is a <a href="tty.html">TTY</a>, then it must be in raw mode.</p> <p>This is automatically called by any readline instance on its <code>input</code> if the <code>input</code> is a terminal. Closing the <code>readline</code> instance does not stop the <code>input</code> from emitting <code>'keypress'</code> events.</p> <pre><code class="language-js">readline.emitKeypressEvents(process.stdin); if (process.stdin.isTTY) process.stdin.setRawMode(true);</code></pre> <h2>readline.moveCursor(stream, dx, dy)<span><a class="mark" href="#readline_readline_movecursor_stream_dx_dy" id="readline_readline_movecursor_stream_dx_dy">#</a></span></h2> <div class="api_metadata"> <span>Added in: v0.7.7</span> </div><ul> <li><code>stream</code> <a href="stream.html#stream_class_stream_writable" class="type"><stream.Writable></a></li> <li><code>dx</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> <li><code>dy</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>The <code>readline.moveCursor()</code> method moves the cursor <em>relative</em> to its current position in a given <a href="tty.html">TTY</a> <code>stream</code>.</p> <h2>Example: Tiny CLI<span><a class="mark" href="#readline_example_tiny_cli" id="readline_example_tiny_cli">#</a></span></h2> <p>The following example illustrates the use of <code>readline.Interface</code> class to implement a small command-line interface:</p> <pre><code class="language-js">const readline = require('readline'); const rl = readline.createInterface({ input: process.stdin, output: process.stdout, prompt: 'OHAI> ' }); rl.prompt(); rl.on('line', (line) => { switch (line.trim()) { case 'hello': console.log('world!'); break; default: console.log(`Say what? I might have heard '${line.trim()}'`); break; } rl.prompt(); }).on('close', () => { console.log('Have a great day!'); process.exit(0); });</code></pre> <h2>Example: Read File Stream Line-by-Line<span><a class="mark" href="#readline_example_read_file_stream_line_by_line" id="readline_example_read_file_stream_line_by_line">#</a></span></h2> <p>A common use case for <code>readline</code> is to consume an input file one line at a time. The easiest way to do so is leveraging the <a href="fs.html#fs_class_fs_readstream"><code>fs.ReadStream</code></a> API as well as a <code>for</code>-<code>await</code>-<code>of</code> loop:</p> <pre><code class="language-js">const fs = require('fs'); const readline = require('readline'); async function processLineByLine() { const fileStream = fs.createReadStream('input.txt'); const rl = readline.createInterface({ input: fileStream, crlfDelay: Infinity }); // Note: we use the crlfDelay option to recognize all instances of CR LF // ('\r\n') in input.txt as a single line break. for await (const line of rl) { // Each line in input.txt will be successively available here as `line`. console.log(`Line from file: ${line}`); } } processLineByLine();</code></pre> <p>Alternatively, one could use the <a href="#readline_event_line"><code>'line'</code></a> event:</p> <pre><code class="language-js">const fs = require('fs'); const readline = require('readline'); const rl = readline.createInterface({ input: fs.createReadStream('sample.txt'), crlfDelay: Infinity }); rl.on('line', (line) => { console.log(`Line from file: ${line}`); });</code></pre> <p>Currently, <code>for</code>-<code>await</code>-<code>of</code> loop can be a bit slower. If <code>async</code> / <code>await</code> flow and speed are both essential, a mixed approach can be applied:</p> <pre><code class="language-js">const { once } = require('events'); const { createReadStream } = require('fs'); const { createInterface } = require('readline'); (async function processLineByLine() { try { const rl = createInterface({ input: createReadStream('big-file.txt'), crlfDelay: Infinity }); rl.on('line', (line) => { // Process the line. }); await once(rl, 'close'); console.log('File processed.'); } catch (err) { console.error(err); } })();</code></pre> </div> </div> </div> <script src="assets/sh_main.js"></script> <script src="assets/sh_javascript.min.js"></script> <script>highlight(undefined, undefined, 'pre');</script> </body> </html>
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