How to read from stdin line by line in Node
I'm looking to process a text file with node using a command line call like:
node app.js < input.txt
Each line of the file needs to be processed individually, but once processed the input line can be forgotten.
Using the on-data listener of the stdin, I get the input steam chunked by a byte size so I set this up.
process.stdin.resume();
process.stdin.setEncoding('utf8');
var lingeringLine = "";
process.stdin.on('data', function(chunk) {
lines = chunk.split("\n");
lines[0] = lingeringLine + lines[0];
lingeringLine = lines.pop();
lines.forEach(processLine);
});
process.stdin.on('end', function() {
processLine(lingeringLine);
});
But this seems so sloppy. Having to massage around the first and last items of the lines array. Is there not a more elegant way to do this?
You can use the readline module to read from stdin line by line:
var readline = require('readline');
var rl = readline.createInterface({
input: process.stdin,
output: process.stdout,
terminal: false
});
rl.on('line', function(line){
console.log(line);
})
// Work on POSIX and Windows
var fs = require("fs");
var stdinBuffer = fs.readFileSync(0); // STDIN_FILENO = 0
console.log(stdinBuffer.toString());
readline
is specifically designed to work with terminal (that is process.stdin.isTTY === true
). There are a lot of modules which provide split functionality for generic streams, like split. It makes things super-easy:
process.stdin.pipe(require('split')()).on('data', processLine)
function processLine (line) {
console.log(line + '!')
}