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<h2>Table of Contents</h2>
<ul>
<li>
<p><span class="stability_2"><a href="#readline_readline">Readline</a></span></p>
<ul>
<li>
<p><a href="#readline_class_interface">Class: Interface</a></p>
<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>
<p><a href="#readline_readline_createinterface_options">readline.createInterface(options)</a></p>
<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>
<p></p><div class="api_stability api_stability_2"><a href="documentation.html#documentation_stability_index">Stability: 2</a> - Stable</div><p></p>
<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>
<p><code>key</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></p>
<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>
<tbody><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>
</tbody></table>
</details>
</div>
<p></p><div class="api_stability api_stability_2"><a href="documentation.html#documentation_stability_index">Stability: 2</a> - Stable</div><p></p>
<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)<a class="srclink" href="https://github.com/nodejs/node/blob/b401aa24d7ab8b1fb804844df70472c3679696b9/lib/readline.js#L1164">[src]</a><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>
<p><code>dir</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></p>
<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)<a class="srclink" href="https://github.com/nodejs/node/blob/b401aa24d7ab8b1fb804844df70472c3679696b9/lib/readline.js#L1184">[src]</a><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)<a class="srclink" href="https://github.com/nodejs/node/blob/b401aa24d7ab8b1fb804844df70472c3679696b9/lib/readline.js#L74">[src]</a><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>
<tbody><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>
</tbody></table>
</details>
</div>
<ul>
<li>
<p><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></p>
<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)<a class="srclink" href="https://github.com/nodejs/node/blob/b401aa24d7ab8b1fb804844df70472c3679696b9/lib/readline.js#L1119">[src]</a><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])<a class="srclink" href="https://github.com/nodejs/node/blob/b401aa24d7ab8b1fb804844df70472c3679696b9/lib/readline.js#L1044">[src]</a><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)<a class="srclink" href="https://github.com/nodejs/node/blob/b401aa24d7ab8b1fb804844df70472c3679696b9/lib/readline.js#L1140">[src]</a><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>
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