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<h2>Table of Contents</h2>
<ul>
<li><a href="#readline_readline">Readline</a><ul>
<li><a href="#readline_class_interface">Class: Interface</a><ul>
<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>
</ul>
</li>
<li><a href="#readline_events">Events</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>
</ul>
</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>
<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></li>
<li><a href="#readline_readline_cursorto_stream_x_y">readline.cursorTo(stream, x, y)</a></li>
<li><a href="#readline_readline_movecursor_stream_dx_dy">readline.moveCursor(stream, dx, dy)</a></li>
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<div id="apicontent">
<h1>Readline<span><a class="mark" href="#readline_readline" id="readline_readline">#</a></span></h1>
<pre class="api_stability_2">Stability: 2 - Stable</pre><p>To use this module, do <code>require('readline')</code>. Readline allows reading of a
stream (such as <a href="process.html#process_process_stdin"><code>process.stdin</code></a>) on a line-by-line basis.
</p>
<p>Note that once you've invoked this module, your Node.js program will not
terminate until you've closed the interface. Here's how to allow your
program to gracefully exit:
</p>
<pre><code>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>
<h2>Class: Interface<span><a class="mark" href="#readline_class_interface" id="readline_class_interface">#</a></span></h2>
<p>The class that represents a readline interface with an input and output
stream.
</p>
<h3>rl.close()<span><a class="mark" href="#readline_rl_close" id="readline_rl_close">#</a></span></h3>
<p>Closes the <code>Interface</code> instance, relinquishing control on the <code>input</code> and
<code>output</code> streams. The <code>'close'</code> event will also be emitted.
</p>
<h3>rl.pause()<span><a class="mark" href="#readline_rl_pause" id="readline_rl_pause">#</a></span></h3>
<p>Pauses the readline <code>input</code> stream, allowing it to be resumed later if needed.
</p>
<p>Note that this doesn't immediately pause the stream of events. Several events may
be emitted after calling <code>pause</code>, including <code>line</code>.
</p>
<h3>rl.prompt([preserveCursor])<span><a class="mark" href="#readline_rl_prompt_preservecursor" id="readline_rl_prompt_preservecursor">#</a></span></h3>
<p>Readies readline for input from the user, putting the current <code>setPrompt</code>
options on a new line, giving the user a new spot to write. Set <code>preserveCursor</code>
to <code>true</code> to prevent the cursor placement being reset to <code>0</code>.
</p>
<p>This will also resume the <code>input</code> stream used with <code>createInterface</code> if it has
been paused.
</p>
<p>If <code>output</code> is set to <code>null</code> or <code>undefined</code> when calling <code>createInterface</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>
<p>Prepends the prompt with <code>query</code> and invokes <code>callback</code> with the user's
response. Displays the query to the user, and then invokes <code>callback</code>
with the user's response after it has been typed.
</p>
<p>This will also resume the <code>input</code> stream used with <code>createInterface</code> if
it has been paused.
</p>
<p>If <code>output</code> is set to <code>null</code> or <code>undefined</code> when calling <code>createInterface</code>,
nothing is displayed.
</p>
<p>Example usage:
</p>
<pre><code>interface.question('What is your favorite food?', (answer) => {
console.log(`Oh, so your favorite food is ${answer}`);
});</code></pre>
<h3>rl.resume()<span><a class="mark" href="#readline_rl_resume" id="readline_rl_resume">#</a></span></h3>
<p>Resumes the readline <code>input</code> stream.
</p>
<h3>rl.setPrompt(prompt)<span><a class="mark" href="#readline_rl_setprompt_prompt" id="readline_rl_setprompt_prompt">#</a></span></h3>
<p>Sets the prompt, for example when you run <code>node</code> on the command line, you see
<code>> </code>, which is Node.js's prompt.
</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>
<p>Writes <code>data</code> to <code>output</code> stream, unless <code>output</code> is set to <code>null</code> or
<code>undefined</code> when calling <code>createInterface</code>. <code>key</code> is an object literal to
represent a key sequence; available if the terminal is a TTY.
</p>
<p>This will also resume the <code>input</code> stream if it has been paused.
</p>
<p>Example:
</p>
<pre><code>rl.write('Delete me!');
// Simulate ctrl+u to delete the line written previously
rl.write(null, {ctrl: true, name: 'u'});</code></pre>
<h2>Events<span><a class="mark" href="#readline_events" id="readline_events">#</a></span></h2>
<h3>Event: 'close'<span><a class="mark" href="#readline_event_close" id="readline_event_close">#</a></span></h3>
<p><code>function () {}</code>
</p>
<p>Emitted when <code>close()</code> is called.
</p>
<p>Also emitted when the <code>input</code> stream receives its <code>'end'</code> event. The <code>Interface</code>
instance should be considered "finished" once this is emitted. For example, when
the <code>input</code> stream receives <code>^D</code>, respectively known as <code>EOT</code>.
</p>
<p>This event is also called if there is no <code>SIGINT</code> event listener present when
the <code>input</code> stream receives a <code>^C</code>, respectively known as <code>SIGINT</code>.
</p>
<h3>Event: 'line'<span><a class="mark" href="#readline_event_line" id="readline_event_line">#</a></span></h3>
<p><code>function (line) {}</code>
</p>
<p>Emitted whenever the <code>input</code> stream receives a <code>\n</code>, usually received when the
user hits enter, or return. This is a good hook to listen for user input.
</p>
<p>Example of listening for <code>'line'</code>:
</p>
<pre><code>rl.on('line', (cmd) => {
console.log(`You just typed: ${cmd}`);
});</code></pre>
<h3>Event: 'pause'<span><a class="mark" href="#readline_event_pause" id="readline_event_pause">#</a></span></h3>
<p><code>function () {}</code>
</p>
<p>Emitted whenever the <code>input</code> stream is paused.
</p>
<p>Also emitted whenever the <code>input</code> stream is not paused and receives the
<code>SIGCONT</code> event. (See events <code>SIGTSTP</code> and <code>SIGCONT</code>)
</p>
<p>Example of listening for <code>'pause'</code>:
</p>
<pre><code>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>
<p><code>function () {}</code>
</p>
<p>Emitted whenever the <code>input</code> stream is resumed.
</p>
<p>Example of listening for <code>'resume'</code>:
</p>
<pre><code>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>
<p><code>function () {}</code>
</p>
<p><strong>This does not work on Windows.</strong>
</p>
<p>Emitted whenever the <code>input</code> stream is sent to the background with <code>^Z</code>,
respectively known as <code>SIGTSTP</code>, and then continued with <code>fg(1)</code>. This event
only emits if the stream was not paused before sending the program to the
background.
</p>
<p>Example of listening for <code>SIGCONT</code>:
</p>
<pre><code>rl.on('SIGCONT', () => {
// `prompt` will automatically resume the stream
rl.prompt();
});</code></pre>
<h3>Event: 'SIGINT'<span><a class="mark" href="#readline_event_sigint" id="readline_event_sigint">#</a></span></h3>
<p><code>function () {}</code>
</p>
<p>Emitted whenever the <code>input</code> stream receives a <code>^C</code>, respectively known as
<code>SIGINT</code>. If there is no <code>SIGINT</code> event listener present when the <code>input</code>
stream receives a <code>SIGINT</code>, <code>pause</code> will be triggered.
</p>
<p>Example of listening for <code>SIGINT</code>:
</p>
<pre><code>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>
<p><code>function () {}</code>
</p>
<p><strong>This does not work on Windows.</strong>
</p>
<p>Emitted whenever the <code>input</code> stream receives a <code>^Z</code>, respectively known as
<code>SIGTSTP</code>. If there is no <code>SIGTSTP</code> event listener present when the <code>input</code>
stream receives a <code>SIGTSTP</code>, the program will be sent to the background.
</p>
<p>When the program is resumed with <code>fg</code>, the <code>'pause'</code> and <code>SIGCONT</code> events will be
emitted. You can use either to resume the stream.
</p>
<p>The <code>'pause'</code> and <code>SIGCONT</code> events will not be triggered if the stream was paused
before the program was sent to the background.
</p>
<p>Example of listening for <code>SIGTSTP</code>:
</p>
<pre><code>rl.on('SIGTSTP', () => {
// This will override SIGTSTP and prevent the program from going to the
// background.
console.log('Caught SIGTSTP.');
});</code></pre>
<h2>Example: Tiny CLI<span><a class="mark" href="#readline_example_tiny_cli" id="readline_example_tiny_cli">#</a></span></h2>
<p>Here's an example of how to use all these together to craft a tiny command
line interface:
</p>
<pre><code>const readline = require('readline');
const rl = readline.createInterface(process.stdin, process.stdout);
rl.setPrompt('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 case for <code>readline</code>'s <code>input</code> option is to pass a filesystem readable
stream to it. This is how one could craft line-by-line parsing of a file:
</p>
<pre><code>const readline = require('readline');
const fs = require('fs');
const rl = readline.createInterface({
input: fs.createReadStream('sample.txt')
});
rl.on('line', function (line) {
console.log('Line from file:', 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>
<p>Clears current line of given TTY stream in a specified direction.
<code>dir</code> should have one of following values:
</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>
<h2>readline.clearScreenDown(stream)<span><a class="mark" href="#readline_readline_clearscreendown_stream" id="readline_readline_clearscreendown_stream">#</a></span></h2>
<p>Clears the screen 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>
<p>Creates a readline <code>Interface</code> instance. Accepts an <code>options</code> Object that takes
the following values:
</p>
<ul>
<li><p><code>input</code> - the readable stream to listen to (Required).</p>
</li>
<li><p><code>output</code> - the writable stream to write readline data to (Optional).</p>
</li>
<li><p><code>completer</code> - an optional function that is used for Tab autocompletion. See
below for an example of using this.</p>
</li>
<li><p><code>terminal</code> - pass <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.
Defaults to checking <code>isTTY</code> on the <code>output</code> stream upon instantiation.</p>
</li>
<li><p><code>historySize</code> - maximum number of history lines retained. Defaults to <code>30</code>.</p>
</li>
</ul>
<p>The <code>completer</code> function is given the current line entered by the user, and
is supposed to return an Array with 2 entries:
</p>
<ol>
<li><p>An Array with matching entries for the completion.</p>
</li>
<li><p>The substring that was used for the matching.</p>
</li>
</ol>
<p>Which ends up looking something like:
<code>[[substr1, substr2, ...], originalsubstring]</code>.
</p>
<p>Example:
</p>
<pre><code>function completer(line) {
var completions = '.help .error .exit .quit .q'.split(' ')
var hits = completions.filter((c) => { return c.indexOf(line) == 0 })
// show all completions if none found
return [hits.length ? hits : completions, line]
}</code></pre>
<p>Also <code>completer</code> can be run in async mode if it accepts two arguments:
</p>
<pre><code>function completer(linePartial, callback) {
callback(null, [['123'], linePartial]);
}</code></pre>
<p><code>createInterface</code> is commonly used with <a href="process.html#process_process_stdin"><code>process.stdin</code></a> and
<a href="process.html#process_process_stdout"><code>process.stdout</code></a> in order to accept user input:
</p>
<pre><code>const readline = require('readline');
const rl = readline.createInterface({
input: process.stdin,
output: process.stdout
});</code></pre>
<p>Once you have a readline instance, you most commonly listen for the
<code>'line'</code> event.
</p>
<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 fires
a <code>'resize'</code> event on the <code>output</code> if/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>
<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>
<p>Move cursor to the specified position in a given TTY stream.
</p>
<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>
<p>Move cursor relative to it's current position in a given TTY stream.
</p>
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