emitKeypressEvents
The readline.emitKeypressEvents()
method causes the given Readable
stream to begin emitting 'keypress'
events corresponding to received input.
Optionally, interface
specifies a readline.Interface
instance for which autocompletion is disabled when copy-pasted input is detected.
If the stream
is a TTY
, then it must be in raw mode.
This is automatically called by any readline instance on its input
if the input
is a terminal. Closing the readline
instance does not stop the input
from emitting 'keypress'
events.
readline.emitKeypressEvents(process.stdin);
if (process.stdin.isTTY)
process.stdin.setRawMode(true);
Example: Tiny CLI
The following example illustrates the use of readline.Interface
class to implement a small command-line interface:
const readline = require('node: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);
});
Example: Read file stream line-by-Line
A common use case for readline
is to consume an input file one line at a time. The easiest way to do so is leveraging the fs.ReadStream
API as well as a for await...of
loop:
const fs = require('node:fs');
const readline = require('node: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();
Alternatively, one could use the 'line'
event:
const fs = require('node:fs');
const readline = require('node:readline');
const rl = readline.createInterface({
input: fs.createReadStream('sample.txt'),
crlfDelay: Infinity,
});
rl.on('line', (line) => {
console.log(`Line from file: ${line}`);
});
Currently, for await...of
loop can be a bit slower. If async
/ await
flow and speed are both essential, a mixed approach can be applied:
const { once } = require('node:events');
const { createReadStream } = require('node:fs');
const { createInterface } = require('node: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);
}
})();
Since
v0.7.7