how to tail multiple files in node.js?

Question

how to tail multiple files in node.js?

when use the following code to tail a file, we can successfully output data.

var spawn = require('child_process').spawn;
var filename = '/logs/error.log';
var tail = spawn("tail", ["-f", filename]);
tail.stdout.on("data", function (data) {
    console.log(data);
});

but when i change filename to "/logs/*.log", i don't find anything output. who can tell me what is the reason? Thanks!

node.js
tail

Answer 1

When typing tail -f /logs/*.log on the console, the expansion of /logs/*.log is handled by the shell; by the time the tail program gets the arguments, they've already been expanded to tail -f /logs/error.log /logs/other.log. You need to do the expansion yourself for Node:

var fs = require('fs');
var spawn = require('child_process').spawn;
var filename = fs.readdirSync('/logs').map(function(file) { return '/logs/' + file });
var tail = spawn("tail", ["-f"].concat(filename));
tail.stdout.on("data", function (data) {
    console.log(data);
});

Answer 2

Because neither tail nor spawn know how to expand file names with wild cards into the set of matching file names. That's normally performed by the shell, so in this case you'll need to do it yourself in code.